Diatom: Difference between revisions
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{{short description|Class of microalgae found in oceans, waterways, and soil}} |
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{{for|a molecule of two atoms|Diatomic molecule}} |
{{for|a molecule of two atoms|Diatomic molecule}} |
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{{Use dmy dates|date=December 2019}} |
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{{Automatic taxobox |
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{{Taxobox |
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| fossil_range = {{fossilrange|Jurassic|Present}} |
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| color = greenyellow |
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| image = Diatoms through the microscope.jpg |
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| image_upright = 1.2 |
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| image_caption = Light microscopy of a sampling of marine diatoms found living between crystals of annual sea ice in Antarctica, showing a multiplicity of sizes and shapes |
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| image_width = 250px |
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| taxon = Bacillariophyceae |
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| image_caption = Marine diatoms |
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| authority = [[Pierre Dangeard|Dangeard]], 1933<ref>Dangeard, P. (1933). ''Traite d'Algologie.'' Paul Lechvalier and Fils, Paris, [https://books.google.com/books?id=mDxVAAAAMAAJ] {{Webarchive|url=https://web.archive.org/web/20151004183804/https://books.google.com/books?id=mDxVAAAAMAAJ |date=4 October 2015 }}.</ref> |
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| domain = [[Eukaryote|Eukaryota]] |
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| subdivision_ranks = Subclasses |
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| kingdom = [[Chromalveolata]] |
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| subdivision_ref = <ref>{{cite WoRMS |author= |year=2024 |title=Bacillariophyceae |id=148899 |access-date=9 May 2024}}</ref> |
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| unranked_regnum = [[SAR supergroup]] |
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| subdivision = *Bacillariophycidae |
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| phylum = [[Heterokont]]ophyta |
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*[[Coscinodiscophycidae]] |
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| classis = '''Bacillariophyceae''' |
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*Fragilariophycidae |
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| classis_authority = [[Pierre Dangeard|Dangeard]], 1933<ref>Dangeard, P. (1933). ''Traite d'Algologie.'' Paul Lechvalier and Fils, Paris, [https://books.google.com/books?id=mDxVAAAAMAAJ].</ref> |
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| synonyms = * Diatomea <small>[[Barthélemy Charles Joseph Dumortier|Dumortier]], 1821</small><ref>{{cite book |last=Dumortier |first=B.-C. |year=1822 |url=http://images.algaebase.org/pdf/AC100CF013cd51B91ERyQ180397B/16499.pdf |title=Commentationes botanicae. Observations botaniques, dédiées à la Société d'Horticulture de Tournay |url-status=dead |archive-url=https://web.archive.org/web/20151006091814/http://images.algaebase.org/pdf/AC100CF013cd51B91ERyQ180397B/16499.pdf |archive-date=6 October 2015 |via=Algaebase |pages=[i], [1]-116, [1, tabl., err.] |location=Tournay |publisher=Imprimerie de Ch. Casterman-Dieu, Rue de pont No. 10}}</ref> |
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| subdivision_ranks = [[Order (biology)|Orders]] |
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* Diatomophyceae <small>[[Gottlob Ludwig Rabenhorst|Rabenhorst]], 1864</small><ref>Rabenhorst, L. ''[https://archive.org/details/floraeuropaeaalg0103rabe Flora europaea algarum aquae dulcis et submarinae]'' (1864–1868). ''Sectio I. Algas diatomaceas complectens, cum figuris generum omnium xylographice impressis'' (1864). pp. 1–359. Lipsiae [Leipzig]: Apud Eduardum Kummerum.</ref> |
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see text |
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* Bacillariae <small>Haeckel, 1878</small><ref>Haeckel, E. (1878). ''[http://caliban.mpipz.mpg.de/haeckel/protistenreich/high/IMG_8499.html Das Protistenreich] {{Webarchive|url=https://web.archive.org/web/20141110205527/http://caliban.mpipz.mpg.de/haeckel/protistenreich/high/IMG_8499.html |date=10 November 2014 }}.''</ref> |
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| synonyms = |
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* Diatomea <small>[[Barthélemy Charles Joseph Dumortier|Dumortier]], 1821</small><ref>Dumortier, B.-C. (1822). ''[http://images.algaebase.org/pdf/AC100CF013cd51B91ERyQ180397B/16499.pdf Commentationes botanicae. Observations botaniques, dédiées à la Société d'Horticulture de Tournay]'' (disponible at Algaebase). pp. [i], [1]-116, [1, tabl., err.]. Tournay: Imprimerie de Ch. Casterman-Dieu, Rue de pont No. 10.</ref> |
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* Diatomophyceae <small>[[Gottlob Ludwig Rabenhorst|Rabenhorst]], 1864</small><ref>Rabenhorst, L. ''[https://archive.org/details/floraeuropaeaalg0103rabe Flora europaea algarum aquae dulcis et submarinae]'' (1864-1868). ''Sectio I. Algas diatomaceas complectens, cum figuris generum omnium xylographice impressis'' (1864). pp. 1-359. Lipsiae [Leipzig]: Apud Eduardum Kummerum.</ref> |
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* Bacillariae <small>Haeckel, 1878</small><ref>Haeckel, E. (1878). ''[http://caliban.mpipz.mpg.de/haeckel/protistenreich/high/IMG_8499.html Das Protistenreich].''</ref> |
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* Bacillariophyta <small>[[Engler system|Engler & Gilg]], 1919</small><ref>Engler, A. & Gilg, E. (1919). ''Syllabus der Pflanzenfamilien: eine Übersicht über das gesamte Pflanzensystem mit besonderer Berücksichtigung der Medizinal- und Nutzpflanzen, nebst einer Übersicht über die Florenreiche und Florengebiete der Erde zum Gebrauch bei Vorlesungen und Studien über spezielle und medizinisch-pharmazeutische Botanik'', 8th ed., Gebrüder Borntraeger Verlag, Berlin, 395 p.</ref> |
* Bacillariophyta <small>[[Engler system|Engler & Gilg]], 1919</small><ref>Engler, A. & Gilg, E. (1919). ''Syllabus der Pflanzenfamilien: eine Übersicht über das gesamte Pflanzensystem mit besonderer Berücksichtigung der Medizinal- und Nutzpflanzen, nebst einer Übersicht über die Florenreiche und Florengebiete der Erde zum Gebrauch bei Vorlesungen und Studien über spezielle und medizinisch-pharmazeutische Botanik'', 8th ed., Gebrüder Borntraeger Verlag, Berlin, 395 p.</ref> |
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'''Diatoms'''<ref>{{LSJ|dia/tomos|''diá-tom-os''}} "cut in half" (= [http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0058%3Aalphabetic+letter%3D*d%3Aentry+group%3D30%3Aentry%3Ddixo%2Ftomos ''dichó-tom-os'']) — {{LSJ|dia/|''diá''}} "through" or "apart" and the root of {{LSJ|te/mnw1|''tém-n-ō''}} "I cut". {{ablaut|e|o||verb root}}</ref> are a major group of [[algae]], and are among the most common types of [[phytoplankton]]. Diatoms are [[unicellular]], although they can form [[Colony (biology)|colonies]] in the shape of filaments or ribbons (e.g. ''Fragilaria''), fans (e.g. ''Meridion''), zigzags (e.g. ''[[Tabellaria]]''), or stars (e.g. ''[[Asterionella]]''). The first diatom formally described in scientific literature, the colonial ''[[Bacillaria paxillifer|Bacillaria paradoxa]]'', was found in 1783 by Danish naturalist [[Otto Friedrich Müller]]. Diatoms are [[Autotroph|producers]] within the [[food chain]]. A unique feature of diatom cells is that they are enclosed within a cell wall made of [[silica]] (hydrated silicon dioxide) called a [[frustule]].<ref>{{cite web | title=More on Diatoms | website=University of California Museum of Paleontology | url = http://www.ucmp.berkeley.edu/chromista/diatoms/diatommm.html}}</ref> These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name. The symmetry is not perfect since one of the valves is slightly larger than the other, allowing one valve to fit inside the edge of the other. [[Fossil]] evidence suggests that they originated during, or before, the early [[Jurassic period]]. Only male gametes of centric diatoms are capable of movement by means of [[flagellum|flagella]]. Diatom communities are a popular tool for [[environmental monitoring|monitoring environmental]] conditions, past and present, and are commonly used in studies of water quality. |
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A '''diatom''' ([[Neo-Latin]] ''diatoma''){{efn|From {{langx|el|διατομή|diatomé}}, "a cutting through, a severance",<ref name="lsjdiatome">{{LSJ|diatomh/|διατομή|ref}}</ref> from {{langx|el|διάτομος|diátomos}}, "cut in half, divided equally" <ref name="lsjdiatomos">{{LSJ|dia/tomos|διάτομος|ref}}</ref> from {{langx|el|διατέμνω| diatémno}}, "to cut in twain".<ref name="lsjdiatemnw">{{LSJ|dia/temnw|διατέμνω|ref}}</ref><ref name="oed71diatom">{{Cite encyclopedia |title=The Compact Oxford English Dictionary |year=1971 |publisher=Clarendon Press |isbn=0918414083}}</ref>{{rp|718}}}} is any member of a large group comprising several [[Genus|genera]] of [[algae]], specifically [[microalgae]], found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's [[Biomass (ecology)|biomass]]: they generate about 20 to 50 percent of the [[oxygen]] produced on the planet each year,<ref>{{cite web |url=https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html |title=The Air You're Breathing? A Diatom Made That |website=[[Live Science]] |date=11 June 2014 |access-date=30 April 2018 |archive-date=30 April 2018 |archive-url=https://web.archive.org/web/20180430115059/https://www.livescience.com/46250-teasing-apart-the-diatom-genome.html |url-status=live}}</ref><ref>{{Cite web |url=https://diatoms.org/what-are-diatoms |title=What are Diatoms? |publisher=Diatoms of North America |access-date=28 January 2020 |archive-url=https://web.archive.org/web/20200125061107/https://diatoms.org/what-are-diatoms |archive-date=25 January 2020 |url-status=dead }}</ref> take in over 6.7 billion tonnes of [[silicon]] each year from the waters in which they live,<ref>{{cite journal | last1=Treguer | first1=P. | last2=Nelson | first2=D. M. | last3=Van Bennekom | first3=A. J. | last4=Demaster | first4=D. J. | last5=Leynaert | first5=A. | last6=Queguiner | first6=B. | year=1995 | title=The Silica Balance in the World Ocean: A Reestimate | bibcode=1995Sci...268..375T | journal=Science | volume=268 | issue=5209| pages=375–9 | doi=10.1126/science.268.5209.375 | pmid=17746543 | s2cid=5672525 }}</ref> and constitute nearly half of the organic material found in the oceans. The [[Protist shell|shells]] of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire [[Amazon basin]] is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African [[Sahara]], much of it from the [[Bodélé Depression]], which was once made up of a system of fresh-water lakes.<ref>{{Cite web|url=https://www.kcl.ac.uk/sspp/departments/geography/people/academic/drake/Research/The-Sahara-Megalakes-Project/Lake-Megachad.aspx|title=King's College London – Lake Megachad|website=www.kcl.ac.uk|language=en-GB|access-date=5 May 2018|archive-date=27 November 2018|archive-url=https://web.archive.org/web/20181127124138/https://www.kcl.ac.uk/sspp/departments/geography/people/academic/drake/Research/The-Sahara-Megalakes-Project/Lake-Megachad.aspx|url-status=live}}</ref><ref>{{cite journal |last1=Bristow |first1=C.S. |author2-link=Karen Hudson-Edwards |last2=Hudson-Edwards |first2=K.A. |last3=Chappell |first3=A. |date=2010 |title=Fertilizing the Amazon and equatorial Atlantic with West African dust |journal=Geophys. Res. Lett. |volume=37 |issue=14|pages=L14807 |doi=10.1029/2010GL043486 |bibcode=2010GeoRL..3714807B |s2cid=128466273 }}</ref> |
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==General biology==<!-- This section is linked from [[Frustule]] --> |
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[[File:20110123 185042 Diatom.jpg|thumb|255px|A diatom. Numbered graduations are 10 micrometres apart]] |
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Diatoms are [[unicellular organism]]s: they occur either as solitary cells or in [[Colony (biology)|colonies]], which can take the shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 2000 micrometers.<ref name="HasleSyvertsen1996" /> In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by [[asexual reproduction|asexual]] [[Fission (biology)#Multiple fission|multiple fission]]; the maximum life span of individual cells is about six days.<ref>{{Cite web | url=https://www.smithsonianmag.com/science-nature/gas-guzzlers-1-106582382/ | title=Gas Guzzlers | access-date=22 May 2018 | archive-date=22 May 2018 | archive-url=https://web.archive.org/web/20180522181520/https://www.smithsonianmag.com/science-nature/gas-guzzlers-1-106582382/ | url-status=live }}</ref> Diatoms have two distinct shapes: a few (''centric diatoms'') are ''radially'' symmetric, while most (''pennate diatoms'') are broadly ''bilaterally'' symmetric. |
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There are more than 200 [[genus|genera]] of living diatoms, and it is estimated that there are approximately 100,000 [[Extant taxon|extant]] [[species]].<ref name="HasleSyvertsen1996">{{cite book|author1=Grethe R. Hasle|author2=Erik E. Syvertsen |author3=Karen A. Steidinger |author4=Karl Tangen|editor=Carmelo R. Tomas|title=Identifying Marine Diatoms and Dinoflagellates|url=http://books.google.com/books?id=KQxPtwonlqoC|accessdate=2013-11-13|date=1996-01-25|publisher=Academic Press|isbn=978-0-08-053441-1|pages=5–385|chapter=Marine Diatoms}}</ref><ref name="RoundCrawford1990">{{cite book|author1=Frank Eric Round|author2=R. M. Crawford|author3=D. G. Mann|title=The Diatoms: Biology & Morphology of the Genera|url=http://books.google.com/books?id=xhLJvNa3hw0C|accessdate=2013-11-13|year=1990|publisher=Cambridge University Press|isbn=978-0-521-36318-1}}</ref><ref name="Lund95">Canter-Lund, H. and Lund, J.W.G. (1995). ''Freshwater Algae: Their microscopic world explained'', Biopress Limited. ISBN 0-948737-25-5.</ref><ref>{{cite journal | last =Mann | first =David G. | title = The species concept in diatoms: Evidences for morphologically distinct, sympatric gamodemes in four epipelic speices | journal =Plant Systematics and Evolution | volume =164 | issue =1–4 | pages =215–237 | publisher =Springer Science+Business Media | year =1989 | url =http://www.springerlink.com/content/n307k3757002213t/| issn =1615-6110 | doi =10.1007/BF00940439 | accessdate = 2013-11-13}}</ref> Diatoms are a widespread group and can be found in the [[ocean]]s, in [[freshwater]], in [[soil]]s and on damp surfaces. Most live [[pelagic]]ally in open water, although some live as surface films at the water-sediment interface ([[benthos|benthic]]), or even under damp atmospheric conditions. They are especially important in oceans, where they are estimated to contribute up to 45% of the total oceanic [[primary production]] of organic material.<ref name="BGCC1">{{cite journal | url=http://www.soes.soton.ac.uk/staff/tt/pdfs/silica.pdf | title=Role of diatoms in regulating the ocean's silicon cycle | author=Yool, Andrew; Tyrrell, Toby | journal=Global Biogeochemical Cycles | year=2003 | volume=17 | issue=4 | pages=1103–1124 | doi=10.1029/2002GB002018|bibcode = 2003GBioC..17.1103Y }}</ref><!-- Mann (1989) does not mention this; moved this citation upward --- mmm, it's in Mann (1999) --> Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.<ref>{{cite journal|doi=10.2307/2406711|last=Lipps|first=J.H.|year=1970|title=Plankton Evolution|jstor=2406711|journal= Diatoms occur in all oceans from the poles to the tropics; polar and subpolar regions contain relatively few species compared with temperate biota. Although tropical regions exhibit the greatest number of species, more abundant populations are found in polar to temperate regions.|pages=1–22|volume=24|issue=1}}</ref><ref name="Horner2002">{{cite book|author=Rita A. Horner|title=A taxonomic guide to some common marine phytoplankton|url=http://books.google.com/books?id=JU8VAQAAIAAJ|accessdate=2013-11-13|year=2002|publisher=Biopress|isbn=978-0-948737-65-7|pages=25–30}}</ref> Though usually [[microscope|microscopic]], some species of diatoms can reach up to 2 millimeters in length. |
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The unique feature of diatoms is that they are surrounded by a [[cell wall]] made of silica (hydrated [[silicon dioxide]]), called a [[frustule]].<ref>{{cite web | title=More on Diatoms | website=University of California Museum of Paleontology | url=http://www.ucmp.berkeley.edu/chromista/diatoms/diatommm.html | access-date=20 May 2015 | archive-url=https://web.archive.org/web/20121004130024/http://www.ucmp.berkeley.edu/chromista/diatoms/diatommm.html | archive-date=4 October 2012 | url-status=dead }}</ref> These frustules produce [[structural coloration]], prompting them to be described as "jewels of the sea" and "living opals". |
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[[File:Diatomeas w.jpg|thumb|300px|right|Several species of fresh-water diatoms.]] |
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Movement in diatoms primarily occurs passively as a result of both [[ocean current]]s and wind-induced water [[turbulence]]; however, male [[gamete]]s of centric diatoms have [[flagellum|flagella]], permitting active movement to seek female gametes. Similar to [[plant]]s, diatoms convert [[light|light energy]] to [[chemical energy]] by [[photosynthesis]], but their chloroplasts were acquired in different ways.<ref name="Hoek">{{cite book |title=Algae: an introduction to Phycology |last1=van den Hoek |first1=C. |last2=Mann |first2=D.G. |last3=Jahns |first3=H.M. |publisher=[[Cambridge University Press]] |year=1995 |isbn=978-0-521-31687-3 |location=Cambridge |pages=165–218}}</ref> |
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Diatoms belong to a large group called the [[heterokont]]s, including both [[autotroph]]s (''e.g.'', [[golden alga]]e, [[kelp]]) and [[heterotroph]]s (''e.g.'', [[water mould]]s). Their yellowish-brown [[chloroplast]]s are typical of heterokonts, having four [[plasma membrane|membranes]] and containing [[biological pigment|pigments]] such as the [[carotenoid]] [[fucoxanthin]]. Individuals usually lack [[flagellum|flagella]], but they are present in male [[gamete]]s of the centric diatoms and have the usual heterokont structure, except they lack the hairs ([[mastigonemes]]) characteristic in other groups. Most diatoms are [[Motility|non-motile]], as their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on [[turbulence|turbulent]] mixing of the upper layers by the [[wind]] to keep them suspended in sunlit surface waters. Some species actively regulate their buoyancy with intracellular [[lipid]]s to counter sinking. |
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Unusually for autotrophic organisms, diatoms possess a [[urea cycle]], a feature that they share with [[animal]]s, although this cycle is used to different metabolic ends in diatoms. The family ''Rhopalodiaceae'' also possess a [[cyanobacteria]]l [[endosymbiont]] called a spheroid body. This endosymbiont has lost its photosynthetic properties, but has kept its ability to perform [[nitrogen fixation]], allowing the diatom to [[Nitrogen fixation|fix atmospheric nitrogen]].<ref>{{Cite journal |pmc=4128115 |year=2014 |last1=Nakayama |first1=T. |title=Complete genome of a nonphotosynthetic cyanobacterium in a diatom reveals recent adaptations to an intracellular lifestyle |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=111 |issue=31 |pages=11407–11412 |last2=Kamikawa |first2=R. |last3=Tanifuji |first3=G. |last4=Kashiyama |first4=Y. |last5=Ohkouchi |first5=N. |last6=Archibald |first6=J. M. |last7=Inagaki |first7=Y. |pmid=25049384 |doi=10.1073/pnas.1405222111 |bibcode=2014PNAS..11111407N |doi-access=free}}</ref> Other diatoms in symbiosis with nitrogen-fixing cyanobacteria are among the genera ''Hemiaulus'', ''Rhizosolenia'' and ''Chaetoceros''.<ref>{{Cite journal |last1=Pierella Karlusich |first1=Juan José |last2=Pelletier |first2=Eric |last3=Lombard |first3=Fabien |last4=Carsique |first4=Madeline |last5=Dvorak |first5=Etienne |last6=Colin |first6=Sébastien |last7=Picheral |first7=Marc |last8=Cornejo-Castillo |first8=Francisco M. |last9=Acinas |first9=Silvia G. |last10=Pepperkok |first10=Rainer |last11=Karsenti |first11=Eric |date=2021-07-06 |title=Global distribution patterns of marine nitrogen-fixers by imaging and molecular methods |journal=Nature Communications |language=en |volume=12 |issue=1 |pages=4160 |doi=10.1038/s41467-021-24299-y |issn=2041-1723 |pmc=8260585 |pmid=34230473 |bibcode=2021NatCo..12.4160P}}</ref> |
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A feature of diatoms is the [[urea cycle]], which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and colleagues. Their findings, published in 2011, that diatoms have a functioning urea cycle was highly significant, since prior to this the urea cycle was thought to have originated with the [[metazoans]] who appeared several hundreds of millions of years after the diatoms. Their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not.<ref>{{Cite web | title =Animal-Like Urea Cycle in Ocean's Tiny Diatoms Enables Marine Phytoplankton to Use Carbon and Nitrogen from Their Environment | work =Science Daily | section = Science News | publisher =Science Daily | date =2011-05-12 | url =http://www.sciencedaily.com/releases/2011/05/110511133553.htm | accessdate = 2013-11-13}}</ref> |
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Dinotoms are diatoms that have become endosymbionts inside [[dinoflagellates]]. Research on the dinoflagellates ''Durinskia baltica'' and ''Glenodinium foliaceum'' has shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimal to no gene loss. The main difference between these and free living diatoms is that they have lost their cell wall of silica, making them the only known shell-less diatoms.<ref>[https://academic.oup.com/mbe/article/33/9/2376/2579291?login=false Functional Relationship between a Dinoflagellate Host and Its Diatom Endosymbiont | Molecular Biology and Evolution | Oxford Academic]</ref> |
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Diatom cells are contained within a unique silica [[cell wall]] comprising two separate valves (or shells).{{citation needed|date=January 2016}} The [[biogenic silica]] composing the cell wall is synthesised [[intracellular]]ly by the [[polymerisation]] of [[silicic acid]] [[monomer]]s. This material is then extruded to the cell exterior and added to the wall. Diatom cell walls are also called [[frustule]]s or "tests", and their two valves typically overlap one over the other like the two halves of a [[petri dish]]. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two halves and grows a smaller half within it. As a result, after each division cycle the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an [[auxospore]]. This expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions.{{citation needed|date=January 2016}} Auxospore production is almost always linked to [[meiosis]] and sexual reproduction. |
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The study of diatoms is a branch of [[phycology]]. Diatoms are classified as [[eukaryote]]s, organisms with a [[nuclear envelope]]-bound [[cell nucleus]], that separates them from the [[prokaryote]]s [[archaea]] and [[bacteria]]. Diatoms are a type of [[plankton]] called [[phytoplankton]], the most common of the plankton types. Diatoms also grow attached to [[benthic zone|benthic]] substrates, floating debris, and on [[aquatic plant|macrophyte]]s. They comprise an integral component of the [[periphyton]] community.<ref>{{cite book |editor-last=Wehr |editor-first=J. D. |editor2-last=Sheath |editor2-first=R. G. |editor3-last=Kociolek |editor3-first=J. P. |year=2015 |title=Freshwater Algae of North America: Ecology and Classification |edition=2nd |location=San Diego |publisher=Academic Press |isbn=978-0-12-385876-4 }}</ref> Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom [[species]] exist. |
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Decomposition and decay of diatoms leads to [[organic matter|organic]] and [[inorganic]] (in the form of [[silicate]]s) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or [[bay mud]]s, since the inorganic matter is embedded in deposition of [[clay]]s and [[silt]]s and forms a permanent [[geological]] record of such marine strata. (See [[siliceous ooze]]). |
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[[Fossil]] evidence suggests that diatoms originated during or before the early [[Jurassic]] period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms is a specimen of extant genus ''Hemiaulus'' in Late Jurassic aged amber from Thailand.<ref>{{Cite journal|last1=Girard|first1=Vincent|last2=Saint Martin|first2=Simona|last3=Buffetaut|first3=Eric|last4=Saint Martin|first4=Jean-Paul|last5=Néraudeau|first5=Didier|last6=Peyrot|first6=Daniel|last7=Roghi|first7=Guido|last8=Ragazzi|first8=Eugenio|last9=Suteethorn|first9=Varavudh|date=2020|title=Thai amber: insights into early diatom history?|journal=BSGF - Earth Sciences Bulletin|volume=191|pages=23|doi=10.1051/bsgf/2020028|issn=1777-5817|doi-access=free}}</ref> |
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The study of diatoms is a branch of [[phycology]], and phycologists specializing in diatoms are called diatomists. |
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Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. [[Diatomaceous earth]] (diatomite) is a collection of diatom shells found in the Earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer. |
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==Classification== |
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[[File:Diatomeas-Haeckel.jpg|thumb|right|Selections from [[Ernst Haeckel]]'s 1904 ''[[Kunstformen der Natur]]'' (Art Forms of Nature), showing pennate (left) and centric (right) frustules.]] |
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[[File:Diatomaceous Earth BrightField.jpg|thumb|right|300px|[[Diatomaceous earth]] as viewed under [[bright field microscopy|bright field]] [[lighting|illumination]] on a [[light microscope]]. Diatomaceous earth is a soft, [[siliceous]], [[sedimentary rock]] made up of the [[cell walls]] of [[diatoms]] and readily crumbles to a fine powder. This sample consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms. This image of diatomaceous earth particles in [[water]] is at a scale of 6.236 pixels/[[μm]], the entire image covers a region of approximately 1.13 by 0.69 mm.]] |
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[[File:Dwindling diatoms and the mixed layer.ogg|thumb|upright=1.8| {{center|'''Dwindling diatoms and the mixed layer'''}} Earth's oceans teem with microscopic plants called [[phytoplankton]]. But according to a 2015 NASA study, populations of diatoms, the largest type of phytoplankton algae, have declined more than 1 percent per year from 1998 to 2012. Phytoplankton are an essential base of the [[marine food web]] and absorb carbon dioxide dissolved in the ocean that originally came from the atmosphere. The tiny organisms occupy the uppermost layer of ocean water, called the [[mixed layer]], where waves and currents continually churn, drawing up nutrients from a deeper layer of water below. Scientists say the phytoplankton declines observed over the 15-year study period are due to the mixed layer becoming shallower, which results in fewer nutrients reaching the diatoms. The reduction in population may reduce the amount of carbon dioxide drawn out of the atmosphere and transferred to the deep ocean for long-term storage.<ref name="NASA 2018">[https://blogs.nasa.gov/earthexpeditions/2018/09/04/the-inner-space-of-the-subarctic-pacific-ocean/ The Inner Space of the Subarctic Pacific Ocean] {{Webarchive|url=https://web.archive.org/web/20201027125701/https://blogs.nasa.gov/earthexpeditions/2018/09/04/the-inner-space-of-the-subarctic-pacific-ocean/ |date=27 October 2020 }} ''NASA Earth Expeditions'', 4 September 2018. {{PD-notice}}</ref><ref>{{cite journal |doi=10.1002/2015GB005139 |title=Recent decadal trends in global phytoplankton composition |year=2015 |last1=Rousseaux |first1=Cecile S. |last2=Gregg |first2=Watson W. |journal=Global Biogeochemical Cycles |volume=29 |issue=10 |pages=1674–1688 |bibcode=2015GBioC..29.1674R |doi-access=free}}</ref>]] |
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The classification of heterokonts is still unsettled, and they may be treated as a [[Division (biology)|division]] (or [[Phylum (biology)|phylum]]), [[Kingdom (biology)|kingdom]], or something in-between. Accordingly, groups like the diatoms may be ranked anywhere from class (usually called '''Diatomophyceae''' or '''Bacillariophyceae''') to division (usually called '''Bacillariophyta'''), with corresponding changes in the ranks of their subgroups. |
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[[File:3D-animation of the diatom Corethron sp.ogg|thumb|upright=1.8| {{center|'''3D-animation of the diatom ''Corethron'' sp.'''<br />Displays overlays from four fluorescent channels}}(a) Green: [DiOC6(3) fluorescence] - stains cellular membranes indicating the core cell bodies<br />(b) Cyan: [PLL-A546 fluorescence] - generic counterstain for visualising eukaryotic cell surfaces<br />(c) Blue: [Hoechst fluorescence] - stains DNA, identifies nuclei<br />(d) Red: [chlorophyll autofluorescence] - resolves chloroplasts{{hsp}}<ref name="Colin 2017">Colin, S., Coelho, L.P., Sunagawa, S., Bowler, C., Karsenti, E., Bork, P., Pepperkok, R. and De Vargas, C. (2017) "Quantitative 3D-imaging for cell biology and ecology of environmental microbial eukaryotes". ''eLife'', '''6''': e26066. {{doi|10.7554/eLife.26066.002}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=16 October 2017 }}.</ref><br /><small> {{center|The animation starts by overlaying all available fluorescent channels, and then clarifies the visualisation by switching channels on and off}}</small>]] |
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Diatoms are traditionally divided into two [[Order (biology)|orders]]: |
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* '''centric''' diatoms ([[Centrales]]), which are radially [[symmetry|symmetrical]] |
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* '''pennate''' diatoms ([[Pennales]]), which are bilaterally symmetrical. The former are [[paraphyletic]] to the latter. |
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==Overview== |
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Due to the difference noted in pennate diatoms, of the presence or absence of a raphe (a longitudinal groove in the valve),<ref>O.E.D. 2nd edition 2005</ref> a more recent classification by Round, Crawford & Mann (1990)<ref name="RoundCrawford1990"/> divides the diatoms (as Bacillarophyta) into three classes and a number of orders:<ref>{{cite web | title =Bacillariophyceae | work =algaebase | publisher =M. D. Guiry | url =http://www.algaebase.org/browse/taxonomy/?id=4337 | accessdate = 2013-11-11}}</ref> |
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Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans.<ref>{{cite journal | last1=Nelson | first1=David M. | last2=Tréguer | first2=Paul | last3=Brzezinski | first3=Mark A. | last4=Leynaert | first4=Aude | last5=Quéguiner | first5=Bernard | title=Production and dissolution of biogenic silica in the ocean: Revised global estimates, comparison with regional data and relationship to biogenic sedimentation | journal=Global Biogeochemical Cycles | publisher=American Geophysical Union (AGU) | volume=9 | issue=3 | year=1995 | issn=0886-6236 | doi=10.1029/95gb01070 | pages=359–372| bibcode=1995GBioC...9..359N }}</ref> This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into the deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species{{hsp}}<ref>{{cite journal | last=Mann | first=David G. | title=The species concept in diatoms | journal=Phycologia | publisher=Informa UK Limited | volume=38 | issue=6 | year=1999 | issn=0031-8884 | doi=10.2216/i0031-8884-38-6-437.1 | pages=437–495| bibcode=1999Phyco..38..437M }}</ref> that are distributed between the two major diatom groups: centrics and pennates.<ref>Simonsen, R., (1979). "The diatom system: ideas on phylogeny", ''Bacillaria'', '''2''': 9–71.</ref><ref name=Moore2017>{{cite journal | last1=Moore | first1=Eric R. | last2=Bullington | first2=Briana S. | last3=Weisberg | first3=Alexandra J. | last4=Jiang | first4=Yuan | last5=Chang | first5=Jeff | last6=Halsey | first6=Kimberly H. | title=Morphological and transcriptomic evidence for ammonium induction of sexual reproduction in Thalassiosira pseudonana and other centric diatoms | journal=PLOS ONE | publisher=Public Library of Science (PLoS) | volume=12 | issue=7 | date=2017-07-07 | issn=1932-6203 | doi=10.1371/journal.pone.0181098 | page=e0181098| pmid=28686696 | pmc=5501676 | bibcode=2017PLoSO..1281098M | doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> |
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==Morphology== |
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*Class [[Coscinodiscophyceae]] Round & R.M.Crawford:<br>centric diatoms |
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Diatoms are generally 20 to 200 micrometers in size,<ref>University College London (2002) [https://www.ucl.ac.uk/GeolSci/micropal/diatom.html#:~:text=Diatoms%20are%20commonly%20between%2020,by%20bands%20into%20long%20chains). Diatoms] {{Webarchive|url=https://web.archive.org/web/20110927231912/http://www.ucl.ac.uk/GeolSci/micropal/diatom.html#:~:text=Diatoms%20are%20commonly%20between%2020,by%20bands%20into%20long%20chains). |date=27 September 2011 }} ''Micropalaeontology Unit''.</ref> with a few larger species. Their yellowish-brown [[chloroplast]]s, the site of photosynthesis, are typical of [[heterokont]]s, having four [[cell membrane]]s and containing [[biological pigment|pigments]] such as the [[carotenoid]] [[fucoxanthin]]. Individuals usually lack [[flagellum|flagella]], but they are present in male [[gamete]]s of the centric diatoms and have the usual heterokont structure, including the hairs ([[mastigoneme]]s) characteristic in other groups. |
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** [[Anaulales]] Round & R.M.Crawford |
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** [[Arachnoidiscales]] Round |
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** [[Asterolamprales]] Round |
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** [[Aulacoseirales]] R.M.Crawford |
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** [[Biddulphiales]] |
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** [[Chaetocerotales]] Round & R.M.Crawfor |
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** [[Chrysanthemodiscales]] Round |
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** [[Corethrales]] Round & R.M.Crawford |
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** [[Coscinodiscales]] Round |
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** [[Cymatosirales]] Round & R.M.Crawford |
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** [[Ethmodiscales]] Round |
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** [[Hemiaulales]] Round & R.M.Crawford |
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** [[Leptocylindrales]] Round & R.M.Crawford |
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** [[Lithodesmiales]] |
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** [[Melosirales]] R.M.Crawford |
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** [[Orthoseirales]] R.M.Crawford |
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** [[Paraliales]] R.M.Crawford |
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** [[Rhizosoleniales]] |
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** [[Stictocyclales]] Round |
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** [[Stictodiscales]] Round & R.M.Crawford |
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** [[Thalassiosirales]] |
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** [[Triceratiales]] Round & R.M.Crawford |
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{{Col-begin}} |
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{{Col-1-of-2}} |
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* Class [[Fragilariophyceae]] F.E.Round:<br>pennate diatoms without a [[raphe]] (araphids) |
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** [[Ardissoneales]] F.E.Round |
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** [[Climacospheniales]] Round |
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** [[Cyclophorales]] Round & R.M.Crawford |
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** [[Fragilariales]] P.C.Silva |
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** [[Licmophorales]] Round |
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** [[Protoraphidales]] Round |
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** [[Rhabdonematales]] Round & R.M.Crawford |
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** [[Rhaphoneidales]] Round |
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** [[Striatellales]] F.E.Round |
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** [[Tabellariales]] Round |
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** [[Thalassionematales]] Round |
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** [[Toxariales]] Round |
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{{Col-2-of-2}} |
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* Class [[Bacillariophyceae]] Haeckel, 1878, ''emend.'' D.G.Mann:<br>pennate diatoms with a raphe (raphids) |
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** [[Achnanthales]] P.C.Silva |
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** [[Bacillariales]] Hendey |
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** [[Cymbellales]] D.G.Mann |
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** [[Dictyoneidales]] D.G.Mann |
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** [[Eunotiales]] P.C.Silva |
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** [[Lyrellales]] D.G.Mann |
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** [[Mastogloiales]] D.G.Mann |
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** [[Naviculales]] Bessey |
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** [[Rhopalodiales]] D.G.Mann |
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** [[Surirellales]] D.G.Mann |
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** [[Thalassiophysales]] D.G.Mann |
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{{Col-end}} |
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It is probable there will be further revisions as understanding of their relationships increases. Medlin & Kaczmarska (2004) propose the following classification for the diatoms:<ref>{{cite journal | last =Medlin | first =Linda K. | last2 =Kaczmarska | first2 =Irena | title =Evolution of the diatoms: V. Morphological and cytological support for the major clades and a taxonomic revision | journal =Phycologia | volume =43 | issue =3 | pages =245–270 | publisher =International Phycological Society | year =2004 | url =http://epic.awi.de/12139/1/Med2004a.pdf | doi =10.2216/i0031-8884-43-3-245.1 | accessdate = 2013-11-13}}</ref> |
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Diatoms are often referred as "jewels of the sea" or "living opals" due to their optical properties.<ref>{{cite journal |doi=10.1038/nnano.2007.152 |pmid=18654305 |title=Biomimetics of photonic nanostructures |journal=Nature Nanotechnology |volume=2 |issue=6 |pages=347–53 |year=2007 |last1=Parker |first1=Andrew R. |last2=Townley |first2=Helen E. |bibcode=2007NatNa...2..347P }}</ref> The biological function of this [[structural coloration]] is not clear, but it is speculated that it may be related to communication, camouflage, thermal exchange and/or UV protection.<ref>{{cite journal |doi=10.1016/j.tibtech.2008.11.003 |pmid=19167770 |title=The Glass Menagerie: Diatoms for novel applications in nanotechnology |journal=Trends in Biotechnology |volume=27 |issue=2 |pages=116–27 |year=2009 |last1=Gordon |first1=Richard |last2=Losic |first2=Dusan |last3=Tiffany |first3=Mary Ann |last4=Nagy |first4=Stephen S. |last5=Sterrenburg |first5=Frithjof A.S. }}</ref> |
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* Bacillaryophyta |
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** Coscinodiscophytina |
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*** Coscinodiscophyceae ('radial centrics') |
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** Bacillariophytina |
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*** Mediophyceae ('polar centrics') |
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*** Bacillariophyceae (pennate diatoms) |
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Diatoms |
Diatoms build intricate hard but porous cell walls called [[frustule]]s composed primarily of [[silica]].<ref name="Horner2002" />{{rp|25–30}} This siliceous wall<ref name="Corning Museum of Glass">{{cite web|title=Glass in Nature|url=http://www.cmog.org/article/glass-nature|publisher=The Corning Museum of Glass|access-date=19 February 2013|archive-url=https://web.archive.org/web/20130307120741/http://www.cmog.org/article/glass-nature|archive-date=7 March 2013|url-status=dead}}</ref> can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species. |
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The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half, the ''hypotheca'', is slightly smaller than the other half, the ''epitheca''. Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical. Their distinguishing feature is a hard mineral shell or frustule composed of opal (hydrated, polymerized silicic acid). |
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Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; [[marine mucilage|mucilage]] pads, stalks or tubes; amorphous masses of mucilage, or by threads of [[chitin]], (polysaccharide) which are secreted through strutted processes of the cell. Major pigments of diatoms are [[chlorophylls]] a and c, [[beta-carotene]], [[fucoxanthin]], diatoxanthin and diadinoxanthin.<ref name="HasleSyvertsen1996"/> Diatoms are mainly photosynthetic. A few, however, are obligate [[heterotrophs]], while others can live heterotrophically in the absence of light, provided an appropriate organic carbon source is available. Storage products are [[chrysolaminarin]] and [[lipids]].<ref name="Horner2002"/> |
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[[File:2023 Diatom.svg|thumb|upright=2|center|{{center|'''Representation of a diatom'''}} {{ordered list| Central nodule|Striae; pores, punctae, spots or dots in a line on the surface that allow nutrients in, and waste out, of the cell | |
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[[Hoek, Mann and Jahns system|Hoek ''et al.'' (1995)]]<ref name="Hoek1995">{{cite book|author1=Christiaan Van Den Hoek|author2=D. G. Mann|author3=H. M. Jahns|title=Algae: An Introduction to Phycology|url=http://books.google.com/books?id=xuUoiFesSHMC|accessdate=2013-11-13|year=1995|publisher=Cambridge University Press|isbn=978-0-521-31687-3}}</ref> also provide a comprehensive coverage of diatom taxonomy. |
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[[Areolae (diatom)|Areola]]; hexagonal or polygonal boxlike perforation with a sieve present on the surface of diatom |[[Raphe]]; slit in the valves |Polar nodule; thickening of wall at the distal ends of the raphe <ref>Taylor, J. C., Harding, W. R. and Archibald, C. (2007). ''An Illustrated Guide to Some Common Diatom Species from South Africa''. Gezina: Water Research Commission. {{ISBN|9781770054844}}.</ref><ref>Mishra, M., Arukha, A.P., Bashir, T., Yadav, D. and Prasad, G.B.K.S. (2017) "All new faces of diatoms: potential source of nanomaterials and beyond". ''Frontiers in microbiology'', '''8''': 1239. {{doi|10.3389/fmicb.2017.01239}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=16 October 2017 }}.</ref>|[[Frustule]]; hard and porous cell wall |[[Pyrenoid]]; center of [[carbon fixation]] |[[Plastid]] membranes (4, secondary red) |Inner membranes |[[Thylakoid]]; site of the [[light-dependent reactions]] of [[photosynthesis]] |[[Oil body]]; storage for triacylglycerols <ref>{{cite journal|journal=Philosophical Transactions of the Royal Society B|last=Maeda|first=Yoshiaki|url=https://doi.org/10.1098/rstb.2016.0408|title=Structure and properties of oil bodies in diatoms|date=2017-07-17|volume=372|issue=1728|doi=10.1098/rstb.2016.0408 |pmid=28717018 |pmc=5516117 }}</ref>|[[Mitochondria|Mitochondrion]]; creates [[Adenosine triphosphate|ATP]] (energy) for the cell |[[Vacuole]]s; vesicle of a cell that contains fluid bound by a membrane |Cytoplasmic strand; holds the nucleus |Protoplasmic bridge| Epivalve|[[Cell nucleus|Nucleus]]; holds the genetic material |[[Endoplasmic reticulum]], the transport network for molecules going to specific parts of the cell||[[Golgi apparatus]]; modifies [[protein]]s and sends them out of the cell |Epicingulum|Hypocingulum|Hypovalve|[[Microtubule]] centre}}]] |
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{{clear}} |
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==Ecology== |
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[[File:Diatomeas-Haeckel.jpg|thumb|upright=1.3|right|Selections from [[Ernst Haeckel]]'s 1904 {{lang|de|[[Kunstformen der Natur]]}} (''Art Forms of Nature''), showing pennate (left) and centric (right) frustules.]] |
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[[File:Oceanic Silicon Cycle Budget.svg|thumb|350px|right|A budget of the ocean's silicon cycle<ref name="AAAS1">{{cite journal | last =Tréguer | first =Paul | last2 =Nelson | first2 =David M. | last3 =Van Bennekom | first3 =Aleido J. | last4 =DeMaster | first4 =David J. | last5 =Leynaert | first5 =Aude | last6 =Quéguiner | first6 =Bernard | title =The Silica Balance in the World Ocean: A Reestimate | journal =Science | volume =268 | issue =5209 | pages =375–379 | publisher =American Association for the Advancement of Science | year =1995 | url =http://www.sciencemag.org/content/268/5209/375.abstract | doi =10.1126/science.268.5209.375 | accessdate = 2013-11-13 | pmid =17746543|bibcode = 1995Sci...268..375T }}</ref>]] |
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[[File:Diatoms+Abundance.png|thumb|300px|right|Regions of high abundance of Diatoms in the ocean]] |
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Diatoms are divided into two groups that are distinguished by the shape of the frustule: the ''centric diatoms'' and the ''pennate diatoms''. |
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[[Plankton]]ic diatoms in freshwater and marine environments typically exhibit a "[[boom and bust]]" (or "'''bloom''' and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (''e.g.'' at the start of spring) their competitive edge<ref name=furnas90>{{cite journal | last =Furnas | first =Miles J. | title =In situ growth rates of marine phytoplankton: approaches to measurement, community and species growth rates | journal =Journal of Plankton Research | volume =12 | issue =6 | pages =1117–1151 | publisher =Oxford Journals | url =http://plankt.oxfordjournals.org/content/12/6/1117.abstract#5085 | doi =10.1093/plankt/12.6.1117 | accessdate = 2013-11-14 | year =1990}}</ref> allows them to quickly dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic [[r-selection|r-strategists]] (''i.e.'' those organisms whose ecology is defined by a high growth rate, ''r''). |
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Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the [[raphe]]s and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces. |
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The freshwater diatom [[Didymosphenia geminata]], commonly known as ''Didymo'' causes severe environmental degradation in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This species is native to Europe and is an invasive alien both in the antipodes and in parts of North America.<ref>[http://alienspecies.royalbcmuseum.bc.ca/eng/species/didymo-rock-snot Didymo, Aliens Among Us.] Virtual Exhibit of the [[Virtual Museum of Canada]]</ref><ref>[http://www.ct.gov/deep/cwp/view.asp?A=4013&Q=476204 DEP Reports Didymo Discovered in the West Branch Farmington River. Retrieved on 2014-01-15.]</ref> The problem is most frequently recorded from Australia and [[Didymo in New Zealand|New Zealand]].<ref>{{cite web |url=http://www.biosecurity.govt.nz/pests/didymo/update-31-10-08| title=Didymo Stakeholder Update - 31 October 2008 | publisher=MAF Biosecurity New Zealand www.biosecurity.govt.nz | accessdate=2013-12-01 }}</ref> |
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Centric diatoms are radially symmetric. They are composed of upper and lower valves – ''epitheca'' and ''hypotheca'' – each consisting of a valve and a girdle band that can easily slide underneath each other and expand to increase cell content over the diatoms progression. The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content. The cytoplasmic layer is home to several organelles, like the chloroplasts and mitochondria. Before the centric diatom begins to expand, its nucleus is at the center of one of the valves and begins to move towards the center of the cytoplasmic layer before division is complete. Centric diatoms have a variety of shapes and sizes, depending on from which axis the shell extends, and if spines are present. |
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When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy '''resting spores'''. Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell [[metabolism]]). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the [[thermocline]]. |
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[[File:Shape classification of diatom frustules.png|thumb|upright=1.3|left| {{center|Shape classification of diatom frustules. The images are 3D models. The actual sizes of the frustules are about 10–80 μm.<ref name="Zhang 2012" />}}]] |
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Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous [[upwelling]]<ref name=dugdale98>{{cite journal | last1 = Dugdale | first1 = R. C. | last2 = Wilkerson | first2 = F. P. | year = 1998 | title = Silicate regulation of new production in the equatorial Pacific upwelling | url = http://www.nature.com/nature/journal/v391/n6664/abs/391270a0.html | journal = Nature | volume = 391 | issue = 6664| pages = 270–273 | doi=10.1038/34630|bibcode = 1998Natur.391..270D }}</ref>), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents. |
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[[File:Structure of diatom frustules.png|thumb|upright=1.3|right|{{center|Structure of a centric diatom frustule <ref name="Zhang 2012">{{cite journal|last1=Zhang|first1=D.|last2=Wang|first2=Y.|last3=Cai|first3=J.|last4=Pan|first4=J.|last5=Jiang|first5=X.|last6=Jiang|first6=Y.|year=2012|title=Bio-manufacturing technology based on diatom micro- and nanostructure|journal=Chinese Science Bulletin|volume=57|issue=30|pages=3836–3849|doi=10.1007/s11434-012-5410-x|bibcode=2012ChSBu..57.3836Z|doi-access=free}}</ref>}}]] |
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{{clear}} |
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==Silicification== |
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In the open ocean, the condition that typically causes diatom (spring) blooms to end is a lack of silicon. Unlike other nutrients, this is a major requirement solely of diatoms, so it is not regenerated in the plankton ecosystem as efficiently as, for instance, [[nitrogen]] or [[phosphorus]] nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus). |
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{{see also|Silicification}} |
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Diatom cells are contained within a unique silica [[cell wall]] known as a [[frustule]] made up of two valves called [[theca]]e, that typically overlap one another.<ref>{{cite web|title=Diatoms|url=http://www.ucl.ac.uk/GeolSci/micropal/diatom.html|access-date=13 February 2016|archive-date=2 February 2016|archive-url=https://web.archive.org/web/20160202141717/http://www.ucl.ac.uk/GeolSci/micropal/diatom.html|url-status=live}}</ref> The [[biogenic silica]] composing the cell wall is [[biosynthesis|synthesised]] [[intracellular]]ly by the [[polymerisation]] of [[silicic acid]] [[monomer]]s. This material is then extruded to the cell exterior and added to the wall. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two-halves and grows a smaller half within it. As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an [[auxospore]], usually through [[meiosis]] and sexual reproduction, but exceptions exist. The auxospore expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions.<ref>[https://books.google.com/books?id=xyFvEAAAQBAJ&dq=diatoms+sexual+reproduction+auxospore+frustule&pg=PA295 The Molecular Life of Diatoms]</ref> |
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Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters<ref name=dugdale98/><ref name=smetacek85>{{cite journal | last1 = Smetacek | first1 = V. S. | year = 1985 | title = Role of sinking in diatom life-history cycles: Ecological, evolutionary and geological significance | url = http://www.springerlink.com/content/t5g25521p5252014/ | journal = Mar Biol. | volume = 84 | issue = 3| pages = 239–251 | doi = 10.1007/BF00392493 }}</ref> (see also the [[biological pump]]). Significantly, they also play a key role in the regulation of the biogeochemical cycle of [[silicon]] in the modern ocean.<ref name="BGCC1"/><ref name="AAAS1"/> |
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[[File:Pennate diatom infected with two chytrid-like fungal pathogens.png|thumb|upright=1.4| [[Pennate diatom]] from an Arctic [[meltpond]], infected with two [[Chytridiomycota|chytrid-like]] [zoo-]sporangium fungal pathogens (in false-colour red). Scale bar = 10 μm.<ref>{{cite journal |doi=10.1038/s42003-020-0891-7 |title=Chytrid fungi distribution and co-occurrence with diatoms correlate with sea ice melt in the Arctic Ocean |year=2020 |last1=Kilias |first1=Estelle S. |last2=Junges |first2=Leandro |last3=Šupraha |first3=Luka |last4=Leonard |first4=Guy |last5=Metfies |first5=Katja |last6=Richards |first6=Thomas A. |journal=Communications Biology |volume=3 |issue=1 |page=183 |pmid=32317738 |pmc=7174370 |s2cid=216033140}}</ref>]] |
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[[File:Diatoms Egge and Aksnes 1992 plot.png|thumb|300px|right|Egge & Aksnes (1992)<ref name=egge92>{{cite journal | last1 = Egge | first1 = J. K. | last2 = Aksnes | first2 = D. L. | year = 1992 | title = Silicate as regulating nutrient in phytoplankton competition | url = http://www.int-res.com/articles/meps/83/m083p281.pdf | format = PDF | journal = Mar Ecol. Prog. Ser. | volume = 83 | issue = | pages = 281–289 | doi = 10.3354/meps083281 }}</ref> figure.]] |
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[[File:20110123 185042 Diatom.jpg|thumb|upright=1.4| Light microscopy of a living diatom. Numbered graduations are 10 micrometres apart]] |
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[[File:Diatoms_from_moss.png|thumb|upright=1.4| Assorted diatoms (unknown species) isolated from moss in Bangalore, India.]] |
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The use of silicon by diatoms is believed by many researchers to be the key to their ecological success. In a now classic study, Egge and Aksnes (1992)<ref name=egge92/> found that diatom dominance of mesocosm communities was directly related to the availability of silicic acid — when concentrations were greater than 2 [[Mole (unit)|µmol]] m<sup>−3</sup>, they found that diatoms typically represented more than 70% of the phytoplankton community. Raven (1983)<ref name=raven83>{{cite journal | last1 = Raven | first1 = J. A. | year = 1983 | title = The transport and function of silicon in plants | url = | journal = Biol. Rev. | volume = 58 | issue = 2| pages = 179–207 | doi=10.1111/j.1469-185X.1983.tb00385.x}}</ref> noted that, relative to organic cell walls, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. Other researchers<ref name=milligan02>{{cite journal | last1 = Milligan | first1 = A. J. | last2 = Morel | first2 = F. M. M. | year = 2002 | title = A proton buffering role for silica in diatoms | url = http://www.sciencemag.org/cgi/content/full/297/5588/1848 | journal = Science | volume = 297 | issue = 5588| pages = 1848–1850 | doi=10.1126/science.1074958 | pmid=12228711|bibcode = 2002Sci...297.1848M }}</ref> have suggested that the biogenic silica in diatom cell walls acts as an effective [[pH]] [[buffering agent]], facilitating the conversion of [[bicarbonate]] to dissolved CO<sub>2</sub> (which is more readily assimilated). Notwithstanding the possible advantages conferred by silicon, diatoms typically have higher growth rates than other algae of a corresponding size.<ref name=furnas90/> |
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The exact mechanism of transferring [[silica]] absorbed by the diatom to the [[cell wall]] is unknown. Much of the sequencing of diatom genes comes from the search for the mechanism of silica uptake and deposition in nano-scale patterns in the [[frustule]]. The most success in this area has come from two species, ''[[Thalassiosira pseudonana]]'', which has become the model species, as the whole genome was sequenced and methods for genetic control were established, and ''Cylindrotheca fusiformis'', in which the important silica deposition proteins silaffins were first discovered.<ref name="hildebrand06">{{cite journal|last1=Thamatrakoln|first1=K.|title=Comparative Sequence Analysis of Diatom Silicon Transporters: Toward a Mechanistic Model of Silicon Transport|last2=Alverson|first2=A. J.|last3=Hildebrand|first3=M.|journal=Journal of Phycology|date=2006|volume=42|issue=4|pages=822–834|doi=10.1111/j.1529-8817.2006.00233.x|bibcode=2006JPcgy..42..822T |s2cid=86674657}}</ref> Silaffins, sets of polycationic [[peptides]], were found in ''C. fusiformis'' cell walls and can generate intricate silica structures. These structures demonstrated pores of sizes characteristic to diatom patterns. When ''T. pseudonana'' underwent genome analysis it was found that it encoded a [[urea cycle]], including a higher number of [[polyamines]] than most genomes, as well as three distinct silica transport genes.<ref>{{cite journal|last1=Kröger|first1=Nils|last2=Deutzmann|first2=Rainer|last3=Manfred|first3=Sumper|s2cid=10925689|title=Polycationic Peptides from Diatom Biosilica That Direct Silica Nanosphere Formation.|journal=Science|date=November 1999|volume=286|issue=5442|pages=1129–1132|doi=10.1126/science.286.5442.1129|pmid=10550045}}{{Dead link|date=March 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> In a [[phylogenetic]] study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species.<ref name="hildebrand06" /> This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms. The sequences compared in this study were used to create a diverse background in order to identify residues that differentiate function in the silica deposition process. Additionally, the same study found that a number of the regions were conserved within species, likely the base structure of silica transport. |
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Diatoms occur in virtually every environment that contains water. This includes not only oceans, seas, lakes and streams, but also soil. |
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These silica transport proteins are unique to diatoms, with no [[homologs]] found in other species, such as sponges or rice. The divergence of these silica transport genes is also indicative of the structure of the protein evolving from two repeated units composed of five membrane bound segments, which indicates either gene duplication or [[Protein dimer|dimerization]].<ref name="hildebrand06" /> The silica deposition that takes place from the membrane bound vesicle in diatoms has been hypothesized to be a result of the activity of silaffins and long chain polyamines. This Silica Deposition Vesicle (SDV) has been characterized as an acidic compartment fused with Golgi-derived vesicles.<ref>{{cite book|last1=Kroger|first1=Nils|title=Handbook of Biomineralization: Biological Aspects and Structure Formation|date=2007|publisher=Wiley-VCH Verlag GmbH|location=Weinheim, Germany|pages=chapter 3}}</ref> These two protein structures have been shown to create sheets of patterned silica [[in-vivo]] with irregular pores on the scale of diatom [[frustules]]. One hypothesis as to how these proteins work to create complex structure is that residues are conserved within the SDV's, which is unfortunately difficult to identify or observe due to the limited number of diverse sequences available. Though the exact mechanism of the highly uniform deposition of silica is as yet unknown, the ''Thalassiosira pseudonana'' genes linked to silaffins are being looked to as targets for genetic control of nanoscale silica deposition. |
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==Life-cycle== |
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[[File:Centric diatom life-cycle.jpg|thumb|200px|Sexual reproduction of a centric diatom ([[oogamy]])]] |
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[[File:Diatom pennate life cycle.jpg|thumb|200px|Sexual reproduction of a pinnate diatom (morphological [[isogamy]], physiological [[anisogamy]])]] |
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The ability of diatoms to make [[silica|silica-based]] [[cell wall]]s has been the subject of fascination for centuries. It started with a microscopic observation by an anonymous English country nobleman in 1703, who observed an object that looked like a chain of regular parallelograms and debated whether it was just crystals of salt, or a plant.<ref>Anonymous (1702). "Two letters from a Gentleman in the Country, relating to Mr. Leeuwenhoek's Letter in Transaction, no. 283.", ''Philos. Trans. R. Soc. Lond. B'', '''23''': 1494–1501.</ref> The viewer decided that it was a plant because the parallelograms didn't separate upon agitation, nor did they vary in appearance when dried or subjected to warm water (in an attempt to dissolve the "salt"). Unknowingly, the viewer's confusion captured the essence of diatoms—mineral utilizing plants. It is not clear when it was determined that diatom cell walls are made of silica, but in 1939 a seminal reference characterized the material as [[silicic acid]] in a "subcolloidal" state<ref>Rogall, E. (1939). "[https://www.jstor.org/stable/23357402 Ueber den feinbau der kieselmembran der diatomeen"], ''Planta'': 279-291.</ref> Identification of the main chemical component of the cell wall spurred investigations into how it was made. These investigations have involved, and been propelled by, diverse approaches including, microscopy, chemistry, biochemistry, [[material characterisation]], [[molecular biology]], [['omics]], and [[transgenic]] approaches. The results from this work have given a better understanding of cell wall formation processes, establishing fundamental knowledge which can be used to create models that contextualise current findings and clarify how the process works.<ref name=Hildebrand2018>{{cite journal | last1=Hildebrand | first1=Mark | last2=Lerch | first2=Sarah J. L. | last3=Shrestha | first3=Roshan P. | title=Understanding Diatom Cell Wall Silicification—Moving Forward | journal=Frontiers in Marine Science | publisher=Frontiers Media SA | volume=5 | date=2018-04-11 | issn=2296-7745 | doi=10.3389/fmars.2018.00125| doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> |
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Reproduction among these organisms is primarily asexual by binary fission, with each daughter cell receiving one of the parent cell's two [[frustule]]s (or [[theca]]). This is used by each daughter cell as the larger frustule (or epitheca) into which a second, small frustule (or hypotheca) is constructed. |
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The process of building a mineral-based cell wall inside the cell, then exporting it outside, is a massive event that must involve large numbers of genes and their protein products. The act of building and [[exocytosing]] this large structural object in a short time period, synched with [[cell cycle]] progression, necessitates substantial physical movements within the cell as well as dedication of a significant proportion of the cell's [[biosynthetic]] capacities.<ref name=Hildebrand2018 /> |
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This form of division results in a size reduction of the daughter cell that received the smaller frustule from the parent and therefore the average cell size of a diatom population decreases, until the cells are about one-third their maximum size.<ref name="HasleSyvertsen1996"/> It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size.<ref name="Werner1977">{{cite book|author=G. Drebes|editor=Dietrich Werner|title=The Biology of Diatoms|url=http://books.google.com/books?id=A4GBA7rlAroC|accessdate=2013-11-14|volume=Volume 13 of Botanical Monographs|date=1 January 1977|publisher=University of California Press|isbn=978-0-520-03400-6|pages=250–283|chapter=Chapter 9: Sexuality}}</ref> Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and [[auxospore]] formation must occur.<ref name="HasleSyvertsen1996"/> Vegetative cells of diatoms are [[diploid]] (2N) and so [[meiosis]] can take place, producing male and female gametes which then fuse to form the [[zygote]]. The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve.<ref name="Horner2002"/> |
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The first characterisations of the biochemical processes and components involved in diatom silicification were made in the late 1990s.<ref>{{cite journal | last1=Hildebrand | first1=Mark | last2=Volcani | first2=Benjamin E. | last3=Gassmann | first3=Walter | last4=Schroeder | first4=Julian I. | title=A gene family of silicon transporters | journal=Nature | publisher=Springer Science and Business Media LLC | volume=385 | issue=6618 | year=1997 | issn=0028-0836 | doi=10.1038/385688b0 | pages=688–689| pmid=9034185 | bibcode=1997Natur.385..688H | s2cid=4266966 }}</ref><ref>{{cite journal | last1=Kröger | first1=Nils | last2=Deutzmann | first2=Rainer | last3=Sumper | first3=Manfred | title=Polycationic Peptides from Diatom Biosilica That Direct Silica Nanosphere Formation | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=286 | issue=5442 | date=1999-11-05 | issn=0036-8075 | doi=10.1126/science.286.5442.1129 | pages=1129–1132| pmid=10550045 }}</ref><ref>{{cite journal | last1=Kröger | first1=Nils | last2=Deutzmann | first2=Rainer | last3=Bergsdorf | first3=Christian | last4=Sumper | first4=Manfred | title=Species-specific polyamines from diatoms control silica morphology | journal=Proceedings of the National Academy of Sciences | volume=97 | issue=26 | date=2000-12-05 | issn=0027-8424 | doi=10.1073/pnas.260496497 | pages=14133–14138| pmid=11106386 | pmc=18883 | bibcode=2000PNAS...9714133K | doi-access=free }}</ref> These were followed by insights into how higher order assembly of silica structures might occur.<ref>{{cite journal | last1=Tesson | first1=Benoit | last2=Hildebrand | first2=Mark | title=Extensive and Intimate Association of the Cytoskeleton with Forming Silica in Diatoms: Control over Patterning on the Meso- and Micro-Scale | journal=PLOS ONE | publisher=Public Library of Science (PLoS) | volume=5 | issue=12 | date=2010-12-10 | issn=1932-6203 | doi=10.1371/journal.pone.0014300 | page=e14300| pmid=21200414 | pmc=3000822 | bibcode=2010PLoSO...514300T | doi-access=free }}</ref><ref>{{cite journal | last1=Tesson | first1=Benoit | last2=Hildebrand | first2=Mark | title=Characterization and Localization of Insoluble Organic Matrices Associated with Diatom Cell Walls: Insight into Their Roles during Cell Wall Formation | journal=PLOS ONE | publisher=Public Library of Science (PLoS) | volume=8 | issue=4 | date=2013-04-23 | issn=1932-6203 | doi=10.1371/journal.pone.0061675 | page=e61675| pmid=23626714 | pmc=3633991 | bibcode=2013PLoSO...861675T | doi-access=free }}</ref><ref>{{cite journal | last1=Scheffel | first1=André | last2=Poulsen | first2=Nicole | last3=Shian | first3=Samuel | last4=Kröger | first4=Nils | title=Nanopatterned protein microrings from a diatom that direct silica morphogenesis | journal=Proceedings of the National Academy of Sciences | volume=108 | issue=8 | date=2011-02-07 | issn=0027-8424 | doi=10.1073/pnas.1012842108 | pages=3175–3180| pmid=21300899 | pmc=3044418 | doi-access=free }}</ref> More recent reports describe the identification of novel components involved in higher order processes, the dynamics documented through real-time imaging, and the genetic manipulation of silica structure.<ref>{{cite journal | last1=Kotzsch | first1=Alexander | last2=Gröger | first2=Philip | last3=Pawolski | first3=Damian | last4=Bomans | first4=Paul H. H. | last5=Sommerdijk | first5=Nico A. J. M. | last6=Schlierf | first6=Michael | last7=Kröger | first7=Nils | title=Silicanin-1 is a conserved diatom membrane protein involved in silica biomineralization | journal=BMC Biology | publisher=Springer Science and Business Media LLC | volume=15 | issue=1 | date=2017-07-24 | page=65 | issn=1741-7007 | doi=10.1186/s12915-017-0400-8| pmid=28738898 | pmc=5525289 | doi-access=free }}</ref><ref>{{cite journal | last1=Tesson | first1=Benoit | last2=Lerch | first2=Sarah J. L. | last3=Hildebrand | first3=Mark | title=Characterization of a New Protein Family Associated With the Silica Deposition Vesicle Membrane Enables Genetic Manipulation of Diatom Silica | journal=Scientific Reports | publisher=Springer Science and Business Media LLC | volume=7 | issue=1 | date=2017-10-18 | page=13457 | issn=2045-2322 | doi=10.1038/s41598-017-13613-8| pmid=29044150 | pmc=5647440 | bibcode=2017NatSR...713457T }}</ref> The approaches established in these recent works provide practical avenues to not only identify the components involved in silica cell wall formation but to elucidate their interactions and spatio-temporal dynamics. This type of holistic understanding will be necessary to achieve a more complete understanding of cell wall synthesis.<ref name=Hildebrand2018 /> |
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Diatoms are mostly [[Motility|non-motile]]; however, sperm found in some species can be [[Flagellum|flagellated]], though motility is usually limited to a gliding motion.<ref name="Horner2002"/> In centric diatoms, the small male [[gametes]] have one [[flagellum]] while the female gametes are large and non-motile ([[Oogamy|oogamous]]). Conversely, in pennate diatoms both gametes lack flagella ([[isogamy|isoogamous]]).<ref name="HasleSyvertsen1996"/> Certain araphid species, that is pennate diatoms without a raphe, have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.<ref name="Werner1977"/> |
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==Behaviour== |
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==Evolutionary history== |
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{{Multiple image |
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|image1=Den Norske Nordhavs-expedition, 1876-1878 (1880-1901) (20671468900)-47.jpg |
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|width1=107 |
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|caption1=''Chaetoceros willei''<br /><small>{{smallcaps|Gran, 1897}}</small> |
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|image2=Den Norske Nordhavs-expedition, 1876-1878 (1880-1901) (20671468900)-48+49.jpg |
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|caption2=''Chaetoceros furcillatus'' <small>{{smallcaps|J.W.Bailey, 1856}}</small> |
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}} |
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Most centric and araphid pennate diatoms are [[Motility|nonmotile]], and their relatively dense cell walls cause them to readily sink. [[Plankton]]ic forms in open water usually rely on [[turbulence|turbulent]] mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains.<ref>{{Citation|last1=Padisák|first1=Judit|date=2003|work=Aquatic Biodiversity: A Celebratory Volume in Honour of Henri J. Dumont|pages=243–257|editor-last=Martens|editor-first=Koen|series=Developments in Hydrobiology|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-007-1084-9_18|isbn=9789400710849|last2=Soróczki-Pintér|first2=Éva|last3=Rezner|first3=Zsuzsanna|title=Sinking properties of some phytoplankton shapes and the relation of form resistance to morphological diversity of plankton — an experimental study |url=http://real.mtak.hu/3305/4/1014414.pdf|access-date=4 October 2019|archive-url=https://web.archive.org/web/20180723003836/http://real.mtak.hu/3305/4/1014414.pdf|archive-date=23 July 2018|url-status=dead}}</ref> These adaptations increase their [[Surface-area-to-volume ratio|surface area to volume ratio]] and [[Parasitic drag|drag]], allowing them to stay suspended in the water column longer. Individual cells may regulate [[buoyancy]] via an ionic pump.<ref>{{cite journal|last1=Anderson|first1=Lars W. J.|last2=Sweeney|first2=Beatrice M.|title=Diel changes in sedimentation characteristics of Ditylum brightwelli: Changes in cellular lipid and effects of respiratory inhibitors and ion-transport modifiers1|journal=Limnology and Oceanography|date=1 May 1977|volume=22|issue=3|pages=539–552|doi=10.4319/lo.1977.22.3.0539|language=en|issn=1939-5590|bibcode=1977LimOc..22..539A|doi-access=free}}</ref> |
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Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive [[mucilage]] secreted through a seamlike structure called the raphe.<ref>{{Cite journal|last1=Poulsen|first1=Nicole C.|last2=Spector|first2=Ilan|last3=Spurck|first3=Timothy P.|last4=Schultz|first4=Thomas F.|last5=Wetherbee|first5=Richard|date=1 September 1999|title=Diatom gliding is the result of an actin-myosin motility system|journal=Cell Motility and the Cytoskeleton |language=en|volume=44|issue=1|pages=23–33|doi=10.1002/(SICI)1097-0169(199909)44:1<23::AID-CM2>3.0.CO;2-D|pmid=10470016|issn=1097-0169}}</ref><ref>{{Cite web|url=http://tolweb.org/raphid_diatoms/125307|title=raphid diatoms|last=Mann|first=David G.|date=February 2010|website=The Tree of Life Web Project|access-date=27 September 2019|archive-date=27 September 2019|archive-url=https://web.archive.org/web/20190927232025/http://tolweb.org/raphid_diatoms/125307|url-status=dead}}</ref> In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to. |
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Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; [[marine mucilage|mucilage]] pads, stalks or tubes; amorphous masses of mucilage; or by threads of [[chitin]] (polysaccharide), which are secreted through strutted processes of the cell. |
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[[File:Den Norske Nordhavs-expedition, 1876-1878 (1880-1901) (20671468900)-cropped.jpg|thumb|upright=1.5|left|Planktonic diatoms such as ''[[Thalassiosira]]'' sp. (56–62), ''[[Asteromphalus]]'' sp. (63), ''[[Aulacoseira]]'' sp. (64–66), and ''[[Chaetoceros]]'' (see twin image above) often grow in chains, and have features such as spines which slow sinking rates by increasing drag.]] |
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[[File:Diatom chain.jpg|thumb|upright=1.8| Some ''[[Thalassiosira]]'' diatoms form chain-like colonies, like these collected near the Antarctic peninsula coast by the schooner of the [[Tara expedition|''Tara'' Oceans Expedition]] for plankton research.<br />This projection of a stack of [[Confocal microscopy|confocal images]] shows the diatoms' [[cell wall]] (cyan), [[chloroplast]]s (red), [[DNA]] (blue), [[Biological membrane|membranes]] and [[organelle]]s (green).]] |
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{{clear}} |
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== Life cycle == |
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{{multiple image |
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| header = Sexual reproduction |
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| image1 = Centric diatom life-cycle.jpg |
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| caption1 = Centric diatom ([[oogamy]]) |
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| image2 = Diatom pennate life cycle.jpg |
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| caption2 = Pennate diatom (morphological [[isogamy]], physiological [[anisogamy]]) |
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===Reproduction and cell size=== |
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Reproduction among these organisms is asexual by [[binary fission]], during which the diatom divides into two parts, producing two "new" diatoms with identical genes. Each new organism receives one of the two [[frustule]]s – one larger, the other smaller – possessed by the parent, which is now called the [[Frustule#Thecae|epitheca]]; and is used to construct a second, smaller frustule, the [[Frustule#Thecae|hypotheca]]. The diatom that received the larger frustule becomes the same size as its parent, but the diatom that received the smaller frustule remains smaller than its parent. This causes the average cell size of this diatom population to decrease.<ref name="HasleSyvertsen1996" /> It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size.<ref name="Werner1977">{{cite book|author=G. Drebes|editor=Dietrich Werner|title=The Biology of Diatoms|chapter-url=https://books.google.com/books?id=A4GBA7rlAroC|access-date=14 November 2013|volume=13|series=Botanical Monographs|date=1 January 1977|publisher=University of California Press|isbn=978-0-520-03400-6|pages=250–283|chapter=Chapter 9: Sexuality|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801020328/https://books.google.com/books?id=A4GBA7rlAroC|url-status=live}}</ref> Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and [[auxospore]] formation must occur.<ref name="HasleSyvertsen1996" /> |
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===Cell division=== |
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Vegetative cells of diatoms are [[diploid]] (2N) and so [[meiosis]] can take place, producing male and female gametes which then fuse to form the [[zygote]]. The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve.<ref name="Horner2002" /> |
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A defining characteristic of all diatoms is their restrictive and bipartite silica cell wall that causes them to progressively shrink during asexual cell division. At a critically small cell size and under certain conditions, [[auxosporulation]] restitutes cell size and prevents [[:Wiktionary:clonal|clonal]] death.<ref>Lewis, W. M., Jr. (1984). "The diatom sex clock and its evolutionary significance". ''The American Naturalist'', '''123'''(1): 73–80</ref><ref>Chepurnov VA, Mann DG, Sabbe K, Vyverman W. (2004). "Experimental studies on sexual reproduction in diatoms". In Jeon KW, ed. ''A Survey of Cell Biology''. International Review of Cytology '''237''': 91–154. London.</ref><ref>Drebes (1977) "Sexuality". In: Werner D, ed. ''The Biology of Diatoms'', Botanical Monographs '''13''' 250–283. Oxford: Blackwell Scientific Publications.</ref><ref>{{cite journal | title=Size reduction, reproductive strategy and the life cycle of a centric diatom | journal=Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences | publisher=The Royal Society | volume=336 | issue=1277 | date=1992-05-29 | issn=0962-8436 | doi=10.1098/rstb.1992.0056 | pages=191–213 | s2cid=86332060 | ref={{sfnref | The Royal Society}}}}</ref><ref>{{cite journal | last1=Koester | first1=Julie A. | last2=Brawley | first2=Susan H. | last3=Karp-Boss | first3=Lee | last4=Mann | first4=David G. | title=Sexual reproduction in the marine centric diatom Ditylum brightwellii (Bacillariophyta) | journal=European Journal of Phycology | publisher=Informa UK Limited | volume=42 | issue=4 | year=2007 | issn=0967-0262 | doi=10.1080/09670260701562100 | pages=351–366| s2cid=80737380 | doi-access=free | bibcode=2007EJPhy..42..351K }}</ref> The entire lifecycles of only a few diatoms have been described and rarely have sexual events been captured in the environment.<ref name=Moore2017 /> |
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===Sexual reproduction=== |
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Most [[eukaryote]]s are capable of [[sexual reproduction]] involving [[meiosis]]. Sexual reproduction appears to be an obligatory phase in the life cycle of diatoms, particularly as cell size decreases with successive vegetative divisions.<ref name="Mouget2009">Mouget JL, Gastineau R, Davidovich O, Gaudin P, Davidovich NA. Light is a key factor in triggering sexual reproduction in the pennate diatom Haslea ostrearia. FEMS Microbiol Ecol. 2009 Aug;69(2):194-201. doi: 10.1111/j.1574-6941.2009.00700.x. Epub 2009 May 6. PMID 19486155</ref> Sexual reproduction involves production of [[gamete]]s and the fusion of gametes to form a [[zygote]] in which maximal cell size is restored.<ref name = Mouget2009/> The signaling that triggers the sexual phase is favored when cells accumulate together, so that the distance between them is reduced and the contacts and/or the perception of chemical cues is facilitated.<ref>Scalco E, Stec K, Iudicone D, Ferrante MI, Montresor M. The dynamics of sexual phase in the marine diatom Pseudo-nitzschia multistriata (Bacillariophyceae). J Phycol. 2014 Oct;50(5):817-28. doi: 10.1111/jpy.12225. Epub 2014 Sep 14. PMID 26988637</ref> |
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An exploration of the [[genome]]s of five diatoms and one diatom [[transcriptome]] led to the identification of 42 [[gene]]s potentially involved in meiosis.<ref name="Patil2019">Patil S, Moeys S, von Dassow P, Huysman MJ, Mapleson D, De Veylder L, Sanges R, Vyverman W, Montresor M, Ferrante MI. Identification of the meiotic toolkit in diatoms and exploration of meiosis-specific SPO11 and RAD51 homologs in the sexual species Pseudo-nitzschia multistriata and Seminavis robusta. BMC Genomics. 2015 Nov 14;16:930. doi: 10.1186/s12864-015-1983-5. Erratum in: BMC Genomics. 2019 Jul 5;20(1):544. PMID 26572248; PMCID: PMC4647503</ref> Thus a meiotic toolkit appears to be conserved in these six diatom species,<ref name = Patil2019/> indicating a central role of meiosis in diatoms as in other eukaryotes. |
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===Sperm motility=== |
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Diatoms are mostly [[Motility|non-motile]]; however, sperm found in some species can be [[Flagellum|flagellated]], though motility is usually limited to a gliding motion.<ref name="Horner2002" /> In centric diatoms, the small male [[gametes]] have one [[flagellum]] while the female gametes are large and non-motile ([[Oogamy|oogamous]]). Conversely, in pennate diatoms both gametes lack flagella ([[isogamy|isogamous]]).<ref name="HasleSyvertsen1996" /> Certain araphid species, that is pennate diatoms without a [[raphe]] (seam), have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.<ref name="Werner1977" /> |
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=== Degradation by microbes === |
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Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using [[hydrolytic]] enzymes to break down the organic algal material.<ref>{{cite journal |doi=10.1038/17351 |id={{INIST|1755031}} |year=1999 |last1=Azam |first1=Farooq |title=Accelerated dissolution of diatom silica by marine bacterial assemblages |journal=Nature |volume=397 |issue=6719 |pages=508–12 |last2=Bidle |first2=Kay D. |bibcode=1999Natur.397..508B |s2cid=4397909 }}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0059977 |pmid=23560063 |pmc=3613400 |title=The Structure of Microbial Community and Degradation of Diatoms in the Deep Near-Bottom Layer of Lake Baikal |journal=PLOS ONE |volume=8 |issue=4 |pages=e59977 |year=2013 |last1=Zakharova |first1=Yulia R. |last2=Galachyants |first2=Yuri P. |last3=Kurilkina |first3=Maria I. |last4=Likhoshvay |first4=Alexander V. |last5=Petrova |first5=Darya P. |last6=Shishlyannikov |first6=Sergey M. |last7=Ravin |first7=Nikolai V. |last8=Mardanov |first8=Andrey V. |last9=Beletsky |first9=Alexey V. |last10=Likhoshway |first10=Yelena V. |bibcode=2013PLoSO...859977Z |doi-access=free }}</ref> |
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== Ecology == |
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{{plankton sidebar|taxonomy}} |
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[[File:Diatoms+Abundance.png|thumb|upright=1.7|right| {{center|Regions of high abundance of diatoms in the ocean}}]] |
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[[File:Diatoms Egge and Aksnes 1992 plot.png|thumb|upright=1.7|right| {{center|Diatom dominance (as a percentage of total cell |
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counts)<br />versus silicate concentration <ref name="Egge 92">{{cite journal |last1=Egge |first1=J. K. |last2=Aksnes |first2=D. L. |year=1992 |title=Silicate as regulating nutrient in phytoplankton competition |journal=Mar. Ecol. Prog. Ser. |volume=83 |pages=281–289 |doi=10.3354/meps083281 |bibcode=1992MEPS...83..281E |doi-access=free}}</ref>}}]] |
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===Distribution=== |
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Diatoms are a widespread group and can be found in the [[ocean]]s, in [[fresh water]], in [[soil]]s, and on damp surfaces. They are one of the dominant components of [[phytoplankton]] in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton.<ref name="Furnas 1990" /> Most live [[pelagic]]ally in open water, although some live as surface films at the water-sediment interface ([[benthos|benthic]]), or even under damp atmospheric conditions. They are especially important in oceans, where a 2003 study found that they contribute an estimated 45% of the total oceanic [[primary production]] of organic material.<ref name="BGCC1">{{cite journal |doi=10.1029/2002GB002018 |title=Role of diatoms in regulating the ocean's silicon cycle |journal=Global Biogeochemical Cycles |volume=17 |issue=4 |year=2003 |last1=Yool |first1=Andrew |last2=Tyrrell |first2=Toby |pages=n/a |bibcode=2003GBioC..17.1103Y |citeseerx=10.1.1.394.3912 |s2cid=16849373 }}</ref> However, a more recent 2016 study estimates that the number is closer to 20%.<ref>{{Cite journal |last1=Malviya |first1=Shruti |last2=Scalco |first2=Eleonora |last3=Audic |first3=Stéphane |last4=Vincent |first4=Flora |last5=Veluchamy |first5=Alaguraj |last6=Poulain |first6=Julie |last7=Wincker |first7=Patrick |last8=Iudicone |first8=Daniele |last9=de Vargas |first9=Colomban |last10=Bittner |first10=Lucie |last11=Zingone |first11=Adriana |last12=Bowler |first12=Chris |date=2016-02-29 |title=Insights into global diatom distribution and diversity in the world's ocean |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=11 |pages=E1516–E1525 |doi=10.1073/pnas.1509523113 |doi-access=free |pmid=26929361 |issn=0027-8424|pmc=4801293 |bibcode=2016PNAS..113E1516M }}</ref> Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.<ref>{{cite journal |doi=10.2307/2406711 |pmid=28563010 |jstor=2406711 |title=Plankton Evolution |journal=Evolution |volume=24 |issue=1 |pages=1–22 |year=1970 |last1=Lipps |first1=Jere H. }}</ref><ref name="Horner2002">{{cite book|author=Rita A. Horner|title=A taxonomic guide to some common marine phytoplankton|url=https://books.google.com/books?id=JU8VAQAAIAAJ|access-date=13 November 2013|year=2002|publisher=Biopress|isbn=978-0-948737-65-7|pages=25–30|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801020312/https://books.google.com/books?id=JU8VAQAAIAAJ|url-status=live}}</ref> |
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===Growth=== |
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[[Plankton]]ic diatoms in freshwater and marine environments typically exhibit a "[[boom and bust]]" (or "''bloom'' and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at the [[Spring (season)|spring]]), their competitive edge and rapid growth rate<ref name="Furnas 1990">{{cite journal |doi=10.1093/plankt/12.6.1117 |id={{INIST|5474600}} |title=In situ growth rates of marine phytoplankton: Approaches to measurement, community and species growth rates |journal=Journal of Plankton Research |volume=12 |issue=6 |pages=1117–51 |year=1990 |last1=Furnas |first1=Miles J. }}</ref> enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic [[r-selection|r-strategists]] (i.e. those organisms whose ecology is defined by a high growth rate, ''r''). |
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===Impact=== |
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The freshwater diatom ''[[Didymosphenia geminata]]'', commonly known as ''Didymo,'' causes severe [[environmental degradation]] in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an [[invasive species]] both in the [[antipodes]] and in parts of [[North America]].<ref>[http://alienspecies.royalbcmuseum.bc.ca/eng/species/didymo-rock-snot "Didymo, Aliens Among Us"]. {{webarchive|url=https://web.archive.org/web/20151007110108/http://alienspecies.royalbcmuseum.bc.ca/eng/species/didymo-rock-snot |date=7 October 2015 }} Virtual Exhibit of the [[Virtual Museum of Canada]]</ref><ref>{{Cite web |url=http://www.ct.gov/deep/cwp/view.asp?A=4013&Q=476204 |title=DEP Reports Didymo Discovered in the West Branch Farmington River |access-date=27 April 2015 |archive-url=https://web.archive.org/web/20150216015753/http://www.ct.gov/deep/cwp/view.asp?A=4013&Q=476204 |archive-date=16 February 2015 |url-status=dead }}</ref> The problem is most frequently recorded from [[Australia]] and [[Didymo in New Zealand|New Zealand]].<ref>{{cite web |title=Didymo Stakeholder Update – 31 October 2008 |url=http://www.biosecurity.govt.nz/pests/didymo/update-31-10-08 |url-status=dead |archive-url=https://web.archive.org/web/20130212200059/http://www.biosecurity.govt.nz/pests/didymo/update-31-10-08 |archive-date=12 February 2013 |access-date=1 December 2013 |publisher=MAF Biosecurity New Zealand}}</ref> |
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When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy ''resting spores''. Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell [[metabolism]]). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the [[thermocline]]. |
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Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous [[upwelling]]<ref name="Dugdale 1998">{{cite journal | last1=Dugdale | first1=R. C. | last2=Wilkerson | first2=F. P. | year=1998 | title=Silicate regulation of new production in the equatorial Pacific upwelling | journal=Nature | volume=391 | issue=6664| pages=270–273 | doi=10.1038/34630|bibcode=1998Natur.391..270D | s2cid=4394149 }}</ref>), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents. |
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In the open ocean, the diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, [[nitrogen]] or [[phosphorus]] nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus). |
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Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters<ref name="Dugdale 1998" /><ref name="Smetacek 1985">{{cite journal | last1=Smetacek | first1=V. S. | year=1985 | title=Role of sinking in diatom life-history cycles: Ecological, evolutionary and geological significance | journal=Mar. Biol. | volume=84 | issue=3| pages=239–251 | doi=10.1007/BF00392493 | bibcode=1985MarBi..84..239S | s2cid=85054779 }}</ref> (see also the [[biological pump]]). Significantly, they also play a key role in the regulation of the [[biogeochemical cycle]] of [[silicon]] in the modern ocean.<ref name="BGCC1" /><ref name="AAAS1" /> |
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===Reason for success=== |
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Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands.{{Citation needed|date=February 2016}} The use of silicon by diatoms is believed by many researchers to be the key to this ecological success. Raven (1983)<ref name="Raven 1983">{{cite journal | last1=Raven | first1=J. A. | year=1983 | title=The transport and function of silicon in plants | journal=Biol. Rev. | volume=58 | issue=2| pages=179–207 | doi=10.1111/j.1469-185X.1983.tb00385.x| s2cid=86067386 }}</ref> noted that, relative to organic [[cell wall]]s, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992)<ref name="Egge 92" /> found that diatom [[ecological dominance|dominance]] of [[mesocosm]] communities was directly related to the availability of silicic acid – when concentrations were greater than 2 [[Mole (unit)|μmol]] m<sup>−3</sup>, they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers<ref name="milligan 2002">{{cite journal | last1=Milligan | first1=A. J. | last2=Morel | first2=F. M. M. | year=2002 | title=A proton buffering role for silica in diatoms | journal=Science | volume=297 | issue=5588| pages=1848–1850 | doi=10.1126/science.1074958 | pmid=12228711|bibcode=2002Sci...297.1848M | s2cid=206507070 }}</ref> have suggested that the biogenic silica in diatom cell walls acts as an effective [[pH]] [[buffering agent]], facilitating the conversion of [[bicarbonate]] to dissolved CO<sub>2</sub> (which is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size.<ref name="Furnas 1990" /> |
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===Sources for collection=== |
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{{Further|topic=the genus of filamentous diatoms|Oscillaria}} |
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Diatoms can be obtained from multiple sources.<ref name="Chamberlain 1901">Chamberlain, C. J. (1901) ''Methods in Plant Histology'', University of Chicago Press.</ref> Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping [[barnacle]]s, [[oyster]] and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. ''[[Cladophora]]'' is frequently covered with ''[[Cocconeis]]'', an elliptically shaped diatom; ''[[Vaucheria]]'' is often covered with small forms. Since diatoms form an important part of the food of [[mollusc]]s, [[tunicate]]s, and [[fish]]es, the [[alimentary tract]]s of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated.<ref name="Chamberlain 1901" /> |
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==Biogeochemistry== |
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<gallery mode="packed" style="float:right" heights="400px"> |
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File:Oceanic Silicon Cycle Budget.svg|'''The modern oceanic silicon cycle'''<br /><small>{{space|9}}Fluxes are in [[Tera-|T]][[Mole (unit)|mol]] Si y<sup>−1</sup> (1 Tmol = 28 million [[tonne|metric tons]] of silicon)</small> |
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</gallery> |
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===Silica cycle=== |
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{{Further|Silica cycle}} |
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The diagram shows the major [[flux]]es of [[silicon]] in the current ocean. Most [[biogenic silica]] in the ocean ([[silica]] produced by [[biomineralisation|biological activity]]) comes from diatoms. Diatoms extract dissolved [[silicic acid]] from surface waters as they grow, and return it to the [[water column]] when they die. Inputs of silicon arrive from above via [[aeolian dust]], from the coasts via rivers, and from below via [[seafloor sediment]] recycling, weathering, and [[hydrothermal vent|hydrothermal activity]].<ref name="AAAS1">{{cite journal |doi=10.1126/science.268.5209.375 |pmid=17746543 |title=The Silica Balance in the World Ocean: A Reestimate |journal=Science |volume=268 |issue=5209 |pages=375–9 |year=1995 |last1=Treguer |first1=P. |last2=Nelson |first2=D. M. |last3=Van Bennekom |first3=A. J. |last4=Demaster |first4=D. J. |last5=Leynaert |first5=A. |last6=Queguiner |first6=B. |bibcode=1995Sci...268..375T |s2cid=5672525 }}</ref> |
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Although diatoms may have existed since the [[Triassic]], the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the [[Phanerozoic]] (before 544 Ma), it is believed that [[bacteria|microbial]] or [[inorganic]] processes weakly regulated the ocean's silicon cycle.<ref name="SchneiderBoston1993">{{cite book |author1=R. Siever |author2=Stephen Henry Schneider |author3=Penelope J. Boston |title=Scientists on Gaia |chapter-url=https://books.google.com/books?id=h83nGwAACAAJ |access-date=14 November 2013 |date=January 1993 |publisher=[[MIT Press]] |isbn=978-0-262-69160-4 |pages=[https://archive.org/details/scientistsongaia0000unse/page/287 287–295] |chapter=Silica in the oceans: biological-geological interplay |url-access=registration |url=https://archive.org/details/scientistsongaia0000unse/page/287}}</ref><ref>{{cite journal |doi=10.1086/320794 |title=Secular Distribution of Biogenic Silica through the Phanerozoic: Comparison of Silica-Replaced Fossils and Bedded Cherts at the Series Level |journal=The Journal of Geology |volume=109 |issue=4 |pages=509–22 |year=2001 |last1=Kidder |first1=David L. |last2=Erwin |first2=Douglas H. |bibcode=2001JG....109..509K |s2cid=128401816 }}</ref><ref name="Grenne 2003">{{cite journal |doi=10.1130/0091-7613(2003)031<0319:PAMSRS>2.0.CO;2 |id={{INIST|14692468}} |year=2003 |volume=31 |issue=4 |pages=319–22 |title=Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits |journal=Geology |last1=Grenne |first1=Tor |last2=Slack |first2=John F. |bibcode=2003Geo....31..319G }}</ref> Subsequently, the cycle appears dominated (and more strongly regulated) by the [[radiolaria]]ns and [[sea sponge|siliceous sponges]], the former as [[zooplankton]], the latter as [[sedentary lifestyle|sedentary]] [[filter-feeder]]s primarily on the [[continental shelf|continental shelves]].<ref>{{cite journal |doi=10.1016/S0012-8252(00)00024-6 |title=Radiolarian palaeoecology and radiolarites: Is the present the key to the past? |journal=Earth-Science Reviews |volume=52 |issue=1 |pages=83–120 |year=2000 |last1=Racki |first1=G |last2=Cordey |first2=Fabrice |bibcode=2000ESRv...52...83R }}</ref> Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms. |
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However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves,<ref name="Maldonado 1999">{{cite journal |doi=10.1038/44560 |id={{INIST|1990263}} |year=1999 |last1=Maldonado |first1=Manuel |title=Decline in Mesozoic reef-building sponges explained by silicon limitation |journal=Nature |volume=401 |issue=6755 |pages=785–8 |last2=Carmona |first2=M. Carmen |last3=Uriz |first3=María J. |last4=Cruzado |first4=Antonio |bibcode=1999Natur.401..785M |s2cid=205034177 }}</ref> suggests that this takeover began in the [[Cretaceous]] (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the [[Cenozoic]] (66 Ma to present).<ref>{{cite journal |doi=10.1130/0091-7613(1975)3<175:SDACRE>2.0.CO;2 |year=1975 |volume=3 |issue=4 |pages=175–177 |title=Silica, diatoms, and Cenozoic radiolarian evolution |journal=Geology |last1=Harper |first1=Howard E. |last2=Knoll |first2=Andrew H. |bibcode=1975Geo.....3..175H }}</ref> |
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{{clear}} |
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<gallery mode="packed" style="float:right" heights="400px"> |
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File:Ocean carbon cycle and diatom carbon dioxide concentration mechanisms 2.jpg|alt=Ocean carbon cycle and diatom carbon dioxide concentration mechanisms|Ocean carbon cycle and diatom carbon dioxide concentration mechanisms{{hsp}}<ref name="Karlusich 2021">{{cite journal | last1=Pierella Karlusich | first1=Juan José | last2=Bowler | first2=Chris | last3=Biswas | first3=Haimanti | title=Carbon Dioxide Concentration Mechanisms in Natural Populations of Marine Diatoms: Insights From Tara Oceans | journal=Frontiers in Plant Science | publisher=Frontiers Media SA | volume=12 | date=2021-04-30 | page=657821 | issn=1664-462X | doi=10.3389/fpls.2021.657821| pmid=33995455 | pmc=8119650 | doi-access=free }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> |
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</gallery> |
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===Carbon cycle=== |
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The diagram depicts some mechanisms by which marine diatoms contribute to the [[biological carbon pump]] and influence the [[ocean carbon cycle]]. The anthropogenic CO<sub>2</sub> emission to the atmosphere (mainly generated by fossil fuel burning and deforestation) is nearly 11 [[gigatonne]] carbon (GtC) per year, of which almost 2.5 GtC is taken up by the surface ocean. In surface seawater ([[pH]] 8.1–8.4), [[bicarbonate]] ({{chem|H|C|O|3|-}}) and [[carbonate]] ions ({{chem|CO|3|2-}}) constitute nearly 90 and <10% of [[dissolved inorganic carbon]] (DIC) respectively, while dissolved CO<sub>2</sub> (CO<sub>2</sub> aqueous) contributes <1%. Despite this low level of CO<sub>2</sub> in the ocean and its slow [[diffusion rate]] in water, diatoms fix 10–20 GtC annually via photosynthesis thanks to their [[carbon dioxide concentrating mechanism]]s, allowing them to sustain [[marine food chain]]s. In addition, 0.1–1% of this organic material produced in the [[euphotic zone|euphotic layer]] sinks down as particles, thus transferring the surface carbon toward the deep ocean and [[Carbon sequestration|sequestering atmospheric CO<sub>2</sub>]] for thousands of years or longer. The remaining [[organic matter]] is [[Remineralisation|remineralized]] through respiration. Thus, diatoms are one of the main players in this biological carbon pump, which is arguably the most important biological mechanism in the Earth System allowing CO<sub>2</sub> to be removed from the [[carbon cycle]] for very long period.<ref name="Friedlingstein etal 2020">{{cite journal | last1=Friedlingstein | first1=Pierre | last2=O'Sullivan | first2=Michael | last3=Jones | first3=Matthew W. | last4=Andrew | first4=Robbie M. | last5=Hauck | first5=Judith | last6=Olsen | first6=Are | last7=Peters | first7=Glen P. | last8=Peters | first8=Wouter | last9=Pongratz | first9=Julia | last10=Sitch | first10=Stephen | last11=Le Quéré | first11=Corinne | last12=Canadell | first12=Josep G. | last13=Ciais | first13=Philippe | last14=Jackson | first14=Robert B. | last15=Alin | first15=Simone | last16=Aragão | first16=Luiz E. O. C. | last17=Arneth | first17=Almut | last18=Arora | first18=Vivek | last19=Bates | first19=Nicholas R. | last20=Becker | first20=Meike | last21=Benoit-Cattin | first21=Alice | last22=Bittig | first22=Henry C. | last23=Bopp | first23=Laurent | last24=Bultan | first24=Selma | last25=Chandra | first25=Naveen | last26=Chevallier | first26=Frédéric | last27=Chini | first27=Louise P. | last28=Evans | first28=Wiley | last29=Florentie | first29=Liesbeth | last30=Forster | first30=Piers M. | last31=Gasser | first31=Thomas | last32=Gehlen | first32=Marion | last33=Gilfillan | first33=Dennis | last34=Gkritzalis | first34=Thanos | last35=Gregor | first35=Luke | last36=Gruber | first36=Nicolas | last37=Harris | first37=Ian | last38=Hartung | first38=Kerstin | last39=Haverd | first39=Vanessa | last40=Houghton | first40=Richard A. | last41=Ilyina | first41=Tatiana | last42=Jain | first42=Atul K. | last43=Joetzjer | first43=Emilie | last44=Kadono | first44=Koji | last45=Kato | first45=Etsushi | last46=Kitidis | first46=Vassilis | last47=Korsbakken | first47=Jan Ivar | last48=Landschützer | first48=Peter | last49=Lefèvre | first49=Nathalie | last50=Lenton | first50=Andrew | last51=Lienert | first51=Sebastian | last52=Liu | first52=Zhu | last53=Lombardozzi | first53=Danica | last54=Marland | first54=Gregg | last55=Metzl | first55=Nicolas | last56=Munro | first56=David R. | last57=Nabel | first57=Julia E. M. S. | last58=Nakaoka | first58=Shin-Ichiro | last59=Niwa | first59=Yosuke | last60=O'Brien | first60=Kevin | last61=Ono | first61=Tsuneo | last62=Palmer | first62=Paul I. | last63=Pierrot | first63=Denis | last64=Poulter | first64=Benjamin | last65=Resplandy | first65=Laure | last66=Robertson | first66=Eddy | last67=Rödenbeck | first67=Christian | last68=Schwinger | first68=Jörg | last69=Séférian | first69=Roland | last70=Skjelvan | first70=Ingunn | last71=Smith | first71=Adam J. P. | last72=Sutton | first72=Adrienne J. | last73=Tanhua | first73=Toste | last74=Tans | first74=Pieter P. | last75=Tian | first75=Hanqin | last76=Tilbrook | first76=Bronte | last77=van der Werf | first77=Guido | last78=Vuichard | first78=Nicolas | last79=Walker | first79=Anthony P. | last80=Wanninkhof | first80=Rik | last81=Watson | first81=Andrew J. | last82=Willis | first82=David | last83=Wiltshire | first83=Andrew J. | last84=Yuan | first84=Wenping | last85=Yue | first85=Xu | last86=Zaehle | first86=Sönke | title=Global Carbon Budget 2020 | journal=Earth System Science Data | publisher=Copernicus GmbH | volume=12 | issue=4 | date=2020-12-11 | issn=1866-3516 | doi=10.5194/essd-12-3269-2020 | pages=3269–3340| bibcode=2020ESSD...12.3269F | display-authors=4| doi-access=free | hdl=10871/126892 | hdl-access=free }}</ref><ref name="Karlusich 2021" /> |
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File:Urea cycle in a diatom.jpg|alt=Mitochondrial urea cycle in a generic diatom cell and the potential fates of urea cycle intermediates| Mitochondrial urea cycle in a generic diatom cell and the potential fates of urea cycle intermediates{{hsp}}<ref name=Glibert2015>{{cite journal | last1=Glibert | first1=Patricia M. | last2=Wilkerson | first2=Frances P. | last3=Dugdale | first3=Richard C. | last4=Raven | first4=John A. | last5=Dupont | first5=Christopher L. | last6=Leavitt | first6=Peter R. | last7=Parker | first7=Alexander E. | last8=Burkholder | first8=JoAnn M. | last9=Kana | first9=Todd M. | display-authors = 6 | title=Pluses and minuses of ammonium and nitrate uptake and assimilation by phytoplankton and implications for productivity and community composition, with emphasis on nitrogen-enriched conditions | journal=Limnology and Oceanography | publisher=Wiley | volume=61 | issue=1 | date=2015-10-11 | issn=0024-3590 | doi=10.1002/lno.10203 | pages=165–197| s2cid=16561857 }} [[File:CC-BY icon.svg|50px]] Modified material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> |
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===Urea cycle=== |
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A feature of diatoms is the [[urea cycle]], which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have a functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the [[metazoans]] which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not.<ref>{{cite journal |doi=10.1038/nature10074 |pmid=21562560 |title=Evolution and metabolic significance of the urea cycle in photosynthetic diatoms |journal=Nature |volume=473 |issue=7346 |pages=203–7 |year=2011 |last1=Allen |first1=Andrew E. |last2=Dupont |first2=Christopher L. |last3=Oborník |first3=Miroslav |last4=Horák |first4=Aleš |last5=Nunes-Nesi |first5=Adriano |last6=McCrow |first6=John P. |last7=Zheng |first7=Hong |last8=Johnson |first8=Daniel A. |last9=Hu |first9=Hanhua |last10=Fernie |first10=Alisdair R. |last11=Bowler |first11=Chris | display-authors = 6 | bibcode=2011Natur.473..203A |s2cid=4350884 |url=http://www.locus.ufv.br/handle/123456789/22722 |access-date=20 May 2021 |archive-date=19 February 2022 |archive-url=https://web.archive.org/web/20220219150348/https://www.locus.ufv.br/handle/123456789/22722 |url-status=live}} |
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*{{cite press release |date=12 May 2011 |title=Animal-like urea cycle in ocean's tiny diatoms enables marine phytoplankton to use carbon and nitrogen from their environment |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2011/05/110511133553.htm}}</ref> |
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While often overlooked in photosynthetic organisms, the [[mitochondria]] also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under [[ammonium]] ({{chem|NH|4|+}}) nutrition compared with [[nitrate]] ({{chem|NO|3|−}}) nutrition. First, in diatoms, and likely some other algae, there is a urea cycle.<ref name=Armbrust2004>{{cite journal | last1=Armbrust | first1=E. Virginia | last2=Berges | first2=John A. | last3=Bowler | first3=Chris | last4=Green | first4=Beverley R. | last5=Martinez | first5=Diego | last6=Putnam | first6=Nicholas H. | last7=Zhou | first7=Shiguo | last8=Allen | first8=Andrew E. | last9=Apt | first9=Kirk E. | last10=Bechner | first10=Michael | last11=Brzezinski | first11=Mark A. | last12=Chaal | first12=Balbir K. | last13=Chiovitti | first13=Anthony | last14=Davis | first14=Aubrey K. | last15=Demarest | first15=Mark S. | last16=Detter | first16=J. Chris | last17=Glavina | first17=Tijana | last18=Goodstein | first18=David | last19=Hadi | first19=Masood Z. | last20=Hellsten | first20=Uffe | last21=Hildebrand | first21=Mark | last22=Jenkins | first22=Bethany D. | last23=Jurka | first23=Jerzy | last24=Kapitonov | first24=Vladimir V. | last25=Kröger | first25=Nils | last26=Lau | first26=Winnie W. Y. | last27=Lane | first27=Todd W. | last28=Larimer | first28=Frank W. | last29=Lippmeier | first29=J. Casey | last30=Lucas | first30=Susan | last31=Medina | first31=Mónica | last32=Montsant | first32=Anton | last33=Obornik | first33=Miroslav | last34=Parker | first34=Micaela Schnitzler | last35=Palenik | first35=Brian | last36=Pazour | first36=Gregory J. | last37=Richardson | first37=Paul M. | last38=Rynearson | first38=Tatiana A. | last39=Saito | first39=Mak A. | last40=Schwartz | first40=David C. | last41=Thamatrakoln | first41=Kimberlee | last42=Valentin | first42=Klaus | last43=Vardi | first43=Assaf | last44=Wilkerson | first44=Frances P. | last45=Rokhsar | first45=Daniel S. | display-authors = 6 | title=The Genome of the Diatom Thalassiosira Pseudonana : Ecology, Evolution, and Metabolism | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=306 | issue=5693 | year=2004 | issn=0036-8075 | doi=10.1126/science.1101156 | pages=79–86| pmid=15459382 | bibcode=2004Sci...306...79A | s2cid=8593895 | url=https://digital.library.unt.edu/ark:/67531/metadc783254/ }}</ref><ref name=Allen2011>{{cite journal | last1=Allen | first1=Andrew E. | last2=Dupont | first2=Christopher L. | last3=Oborník | first3=Miroslav | last4=Horák | first4=Aleš | last5=Nunes-Nesi | first5=Adriano | last6=McCrow | first6=John P. | last7=Zheng | first7=Hong | last8=Johnson | first8=Daniel A. | last9=Hu | first9=Hanhua | last10=Fernie | first10=Alisdair R. | last11=Bowler | first11=Chris | display-authors = 6 | title=Evolution and metabolic significance of the urea cycle in photosynthetic diatoms | journal=Nature | publisher=Springer Science and Business Media LLC | volume=473 | issue=7346 | year=2011 | issn=0028-0836 | doi=10.1038/nature10074 | pages=203–207| pmid=21562560 | bibcode=2011Natur.473..203A | s2cid=4350884 | url=http://repositorio.uptc.edu.co/handle/001/3087 }}</ref><ref>{{cite journal | last1=Weyman | first1=Philip D. | last2=Beeri | first2=Karen | last3=Lefebvre | first3=Stephane C. | last4=Rivera | first4=Josefa | last5=McCarthy | first5=James K. | last6=Heuberger | first6=Adam L. | last7=Peers | first7=Graham | last8=Allen | first8=Andrew E. | last9=Dupont | first9=Christopher L. | display-authors = 6 | title=Inactivation of P haeodactylum tricornutum urease gene using transcription activator-like effector nuclease-based targeted mutagenesis | journal=Plant Biotechnology Journal | publisher=Wiley | volume=13 | issue=4 | date=2014-10-10 | issn=1467-7644 | doi=10.1111/pbi.12254 | pages=460–470| pmid=25302562 | doi-access=free }}</ref> The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by [[Amino acid#Catabolism|amino acid Catabolism]]; like [[photorespiration]], the urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the [[cytoplasm]], and potentially the [[plastid]]{{hsp}}<ref>{{cite journal | last1=Bender | first1=Sara J. | last2=Parker | first2=Micaela S. | last3=Armbrust | first3=E. Virginia | title=Coupled Effects of Light and Nitrogen Source on the Urea Cycle and Nitrogen Metabolism over a Diel Cycle in the Marine Diatom Thalassiosira pseudonana | journal=Protist | publisher=Elsevier BV | volume=163 | issue=2 | year=2012 | issn=1434-4610 | doi=10.1016/j.protis.2011.07.008 | pages=232–251| pmid=21873112 }}</ref> and may help to regulate ammonium metabolism.<ref name=Armbrust2004 /><ref name=Allen2011 /> Because of this cycle, marine diatoms, in contrast to [[chlorophyte]]s, also have acquired a mitochondrial [[urea transporter]] and, in fact, based on [[bioinformatics]], a complete mitochondrial [[Glutamate synthase|GS-GOGAT]] cycle has been hypothesised.<ref name=Allen2011 /><ref name=Glibert2015 /> |
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===Other=== |
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Diatoms are mainly photosynthetic; however a few are obligate [[heterotrophs]] and can live in the absence of light provided an appropriate organic carbon source is available.<ref>{{Cite journal|last1=Armstrong|first1=E|last2=Rogerson|first2=A|last3=Leftley|first3=Jw|date=2000|title=Utilisation of seaweed carbon by three surface-associated heterotrophic protists, Stereomyxa ramosa, Nitzschia alba and Labyrinthula sp.|journal=Aquatic Microbial Ecology|language=en|volume=21|pages=49–57|doi=10.3354/ame021049|issn=0948-3055|doi-access=free}}</ref><ref>{{Cite journal|last1=Lewin|first1=Joyce|last2=Lewin|first2=R. A.|date=1967|title=Culture and Nutrition of Some Apochlorotic Diatoms of the Genus Nitzschia|journal=Microbiology|volume=46|issue=3|pages=361–367|doi=10.1099/00221287-46-3-361|issn=1350-0872|doi-access=free}}</ref> |
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Photosynthetic diatoms that find themselves in an environment absent of oxygen and/or sunlight can switch to anaerobic respiration known as [[Dissimilatory nitrate reduction to ammonium|nitrate respiration]] (DNRA), and stay dormant for up till months and decades.<ref>{{cite journal | pmid=21402908 | year=2011 | last1=Kamp | first1=A. | last2=De Beer | first2=D. | last3=Nitsch | first3=J. L. | last4=Lavik | first4=G. | last5=Stief | first5=P. | title=Diatoms respire nitrate to survive dark and anoxic conditions | journal=Proceedings of the National Academy of Sciences of the United States of America | volume=108 | issue=14 | pages=5649–5654 | doi=10.1073/pnas.1015744108 | pmc=3078364 | bibcode=2011PNAS..108.5649K | doi-access=free }}</ref><ref>{{Cite journal |title=Nitrate respiration and diel migration patterns of diatoms are linked in sediments underneath a microbial mat |year=2021 |doi=10.1111/1462-2920.15345 |last1=Merz |first1=Elisa |last2=Dick |first2=Gregory J. |last3=Beer |first3=Dirk |last4=Grim |first4=Sharon |last5=Hübener |first5=Thomas |last6=Littmann |first6=Sten |last7=Olsen |first7=Kirk |last8=Stuart |first8=Dack |last9=Lavik |first9=Gaute |last10=Marchant |first10=Hannah K. |last11=Klatt |first11=Judith M. | display-authors = 6 | journal=Environmental Microbiology |volume=23 |issue=3 |pages=1422–1435 |pmid=33264477 |s2cid=227259897 |doi-access=free |bibcode=2021EnvMi..23.1422M |hdl=2027.42/167035 |hdl-access=free }}</ref> |
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Major [[pigment]]s of diatoms are [[chlorophylls]] a and c, [[beta-carotene]], [[fucoxanthin]], diatoxanthin and diadinoxanthin.<ref name="HasleSyvertsen1996" /> |
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==Taxonomy== |
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[[File:Diatomeas w.jpg|thumb|right|{{center|Light microscopy of several species of living freshwater diatoms}}]] |
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[[File:Detail, CSIRO ScienceImage 7632 SEM diatom (cropped).jpg|thumb|{{center|Centric diatom}}]] |
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[[File:CSIRO ScienceImage 7233 diatom.jpg|thumb|{{center|Linked diatoms}}]] |
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[[File:"Diatoms cake". Typical diatom species - Stephanodiscus hantzschii Grunow in Cleve & Grunow.JPG|thumb| {{center|[[Thalassiosirales]]<br />''Stephanodiscus hantzschii''}}]] |
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[[File:Diatom - Isthmia nervosa - 400x (16237138292).jpg|thumb| {{center|[[Coscinodiscophyceae]]<br />''Isthmia nervosaIsthmia nervosa''}}]] |
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[[File:Odontella aurita cells.jpg|thumb| {{center|[[Coscinodiscophyceae]]<br />''Odontella aurita''}}]] |
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{{main|Taxonomy of diatoms}} |
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Diatoms belong to a large group of protists, many of which contain plastids rich in chlorophylls a and c. The group has been variously referred to as [[heterokont]]s, [[chrysophyte]]s, [[chromist]]s or [[stramenopile]]s. Many are [[autotroph]]s such as [[golden alga]]e and [[kelp]]; and [[heterotroph]]s such as [[water mould]]s, opalinids, and actinophryid heliozoa. The classification of this area of protists is still unsettled. In terms of rank, they have been treated as a [[Division (botany)|division]], [[phylum]], [[Kingdom (taxonomy)|kingdom]], or something intermediate to those. Consequently, diatoms are ranked anywhere from a class, usually called '''Diatomophyceae''' or '''Bacillariophyceae''', to a division (=phylum), usually called '''Bacillariophyta''', with corresponding changes in the ranks of their subgroups. |
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===Genera and species=== |
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An estimated 20,000 [[Extant taxon|extant]] diatom [[species]] are believed to exist, of which around 12,000 have been named to date according to Guiry, 2012<ref>{{cite journal |doi=10.1111/j.1529-8817.2012.01222.x|title=How many species of algae are there? |journal=Journal of Phycology |volume=48 |issue=5 |pages=1057–1063 |year=2012 |last1=Guiry |first1=M. D. |pmid=27011267|bibcode=2012JPcgy..48.1057G |s2cid= 30911529}}</ref> (other sources give a wider range of estimates<ref name="HasleSyvertsen1996">{{cite book|first1=Grethe R. |last1=Hasle|first2=Erik E. |last2=Syvertsen|first3=Karen A. |last3=Steidinger|first4=Karl |last4=Tangen|editor-first=Carmelo R. |editor-last=Tomas|title=Identifying Marine Diatoms and Dinoflagellates|chapter-url=https://books.google.com/books?id=KQxPtwonlqoC|access-date=13 November 2013|date=25 January 1996|publisher=Academic Press|isbn=978-0-08-053441-1|pages=5–385|chapter=Marine Diatoms|archive-date=3 January 2014|archive-url=https://web.archive.org/web/20140103085057/http://books.google.com/books?id=KQxPtwonlqoC|url-status=live}}</ref><ref name="RoundCrawford1990">{{cite book|first1=Frank Eric |last1=Round|first2=R. M. |last2=Crawford|first3=D. G. |last3=Mann|title=The Diatoms: Biology & Morphology of the Genera|url=https://books.google.com/books?id=xhLJvNa3hw0C|access-date=13 November 2013|year=1990|publisher=Cambridge University Press|isbn=978-0-521-36318-1|archive-date=24 May 2021|archive-url=https://web.archive.org/web/20210524082251/https://books.google.com/books?id=xhLJvNa3hw0C|url-status=live}}{{page needed|date=March 2017}}</ref><ref name="Lund95">Canter-Lund, H. and Lund, J. W. G. (1995). ''Freshwater Algae: Their microscopic world explained'', Biopress Limited. {{ISBN|0-948737-25-5}}.{{page needed|date=March 2017}}</ref><ref>{{cite journal |doi=10.1007/BF00940439 |jstor=23675282 |title=The species concept in diatoms: Evidence for morphologically distinct, sympatric gamodemes in four epipelic species |journal=Plant Systematics and Evolution |volume=164 |issue=1/4 |pages=215–37 |year=2005 |last1=Mann |first1=David G. |s2cid=37684109 }}</ref>). Around 1,000–1,300 diatom genera have been described, both extant and fossil,<ref>{{cite journal |doi= 10.1080/0269249X.1999.9705462|title=Catalogue of the Diatom Genera |journal=Diatom Research |volume=14 |issue=1 |pages=1–190 |year=1999 |last1=Fourtanier |first1=Elisabeth |last2=Kociolek |first2=J. Patrick|bibcode=1999DiaRe..14....1F }}</ref><ref>The [[World Register of Marine Species]] lists 1,356 diatom genus names from all habitats as at July 2020, of which 1,248 are "accepted".</ref> of which some 250–300 exist only as fossils.<ref>Queries to the World Register of Marine Species, July 2020, return 299 "fossil only" genus names, of which 285 are "accepted".</ref> |
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===Classes and orders=== |
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For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms ([[Centrales]] and [[Pennales]]). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class [[Coscinodiscophyceae]], but splitting the former pennate diatoms into 2 separate classes, [[Fragilariophyceae]] and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new. |
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Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as [[AlgaeBase]], the [[World Register of Marine Species]] and its contributing database [[DiatomBase]], and the system for "all life" represented in Ruggiero et al., 2015, all retain the Round et al. treatment as their basis, albeit with diatoms as a whole treated as a class rather than division/phylum, and Round et al.'s classes reduced to subclasses, for better agreement with the treatment of phylogenetically adjacent groups and their containing taxa. (For references refer the individual sections below). |
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One proposal, by [[Linda Medlin]] and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae-Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 ''Handbook of the Protists'' edited by Archibald et al., with some modifications reflecting the apparent non-monophyly of Medlin et al. original "Coscinodiscophyceae". Meanwhile, a group led by E.C. Theriot favours a different hypothesis of phylogeny, which has been termed the structural gradation hypothesis (SGH) and does not recognise the Mediophyceae as a monophyletic group, while another analysis, that of Parks et al., 2018, finds that the radial centric diatoms (Medlin et al.'s Coscinodiscophyceae) are not monophyletic, but supports the monophyly of Mediophyceae minus ''[[Attheya]]'', which is an anomalous genus. Discussion of the relative merits of these conflicting schemes continues by the various parties involved.<ref>{{cite journal |doi=10.5091/plecevo.2010.418 |title=The limits of nuclear-encoded SSU rDNA for resolving the diatom phylogeny |journal=European Journal of Phycology |volume=4 |issue=3 |pages=277–290 |year=2009 |last1=Theriot |first1=Edward C. |last2=Cannone |first2=Jamie J. |last3=Gutell |first3=Robin R. |last4=Alverson |first4=Andrew J.|pmid=20224747 |pmc=2835975 }}</ref><ref>{{cite journal |doi=10.1080/09670260902749159 |title=A preliminary multigene phylogeny of the diatoms (Bacillariophyta): challenges for future research |journal=Plant Ecology and Evolution |volume=143 |issue=3 |year=2010 |last1=Theriot |first1=Edward C. |last2=Ashworth |first2=Matt |last3=Ruck |first3=Elizabeth |last4=Nakov |first4=Teofil |last5=Jansen |first5=Robert K. |pages=277–290 |pmid=20224747 |pmc=2835975 |doi-access=free }}</ref><ref>{{cite journal |doi=10.1093/molbev/msx268 |title=Signal, uncertainty, and conflict in phylogenomic data for a diverse lineage of microbial eukaryotes (Diatoms, Bacillariophyta) |journal=Molecular Biology and Evolution |volume=35 |issue=1 |pages=80–93 |year=2018 |last1=Parks |first1=Matthew B. |last2=Wickett |first2=Norman J. |last3=Alverson |first3=Andrew J. |pmid=29040712 |pmc=5850769 |doi-access=free }}</ref><ref>{{cite journal |title=Review of the phylogenetic reconstruction of the diatoms using molecular tools with an analysis of a seven gene data set using multiple outgroups and morphological data for a total evidence approach |journal=Phycologia |volume=in press |year=2020 |last1=Medlin |first1=L.K. |last2=Desdevises |first2=Y. |url=http://plymsea.ac.uk/id/eprint/8938/1/PH20-10_R1.pdf |access-date=20 July 2020 |archive-date=20 July 2020 |archive-url=https://web.archive.org/web/20200720012627/http://plymsea.ac.uk/id/eprint/8938/1/PH20-10_R1.pdf |url-status=live }}</ref> |
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====Adl et al., 2019 treatment==== |
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In 2019, Adl ''et al.''<ref name="Adl 2018">{{Cite journal |last1=Adl |first1=Sina M. |last2=Bass |first2=David |last3=Lane|first3=Christopher E. |last4=Lukeš |first4=Julius |last5=Schoch |first5=Conrad L. |last6=Smirnov |first6=Alexey |last7=Agatha |first7=Sabine |last8=Berney |first8=Cedric |last9=Brown |first9=Matthew W. | display-authors = 6 | date=2018-09-26 |title=Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes|journal=Journal of Eukaryotic Microbiology |volume=66 |issue=1 |pages=4–119 |doi=10.1111/jeu.12691|pmid=30257078 |pmc=6492006 }}</ref> presented the following classification of diatoms, while noting: "This revision reflects numerous advances in the phylogeny of the diatoms over the last decade. Due to our poor taxon sampling outside of the Mediophyceae and pennate diatoms, and the known and anticipated diversity of all diatoms, many clades appear at a high classification level (and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed). |
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* Clade [[Diatomista]] Derelle et al. 2016, emend. Cavalier-Smith 2017 (diatoms plus a subset of other ochrophyte groups) |
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** Phylum Diatomeae Dumortier 1821 [= [[Bacillariophyta]] Haeckel 1878] (diatoms) |
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*** Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019 |
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**** Class [[Leptocylindrophyceae]] D.G. Mann in Adl et al. 2019 (''[[Leptocylindrus]]'', ''[[Tenuicylindrus]]'') |
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**** Class [[Corethrophyceae]] D.G. Mann in Adl et al. 2019 (''[[Corethron]]'') |
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*** Subphylum Ellerbeckiophytina D.G. Mann in Adl et al. 2019 (''[[Ellerbeckia]]'') |
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*** Subphylum Probosciophytina D.G. Mann in Adl et al. 2019 (''[[Proboscia]]'') |
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*** Subphylum Melosirophytina D.G. Mann in Adl et al. 2019 (''[[Aulacoseira]]'', ''[[Melosira]]'', ''[[Hyalodiscus]]'', ''[[Stephanopyxis]]'', ''[[Paralia (diatom genus)|Paralia]]'', ''[[Endictya]]'') |
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*** Subphylum Coscinodiscophytina Medlin & Kaczmarska 2004, emend. (''[[Actinoptychus]]'', ''[[Coscinodiscus]]'', ''[[Actinocyclus]]'', ''[[Asteromphalus]]'', ''[[Aulacodiscus]]'', ''[[Stellarima]]'') |
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*** Subphylum Rhizosoleniophytina D.G. Mann in Adl et al. 2019 (''[[Guinardia]]'', ''[[Rhizosolenia]]'', ''[[Pseudosolenia]]'') |
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*** Subphylum Arachnoidiscophytina D.G. Mann in Adl et al. 2019 (''[[Arachnoidiscus]]'') |
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*** Subphylum Bacillariophytina Medlin & Kaczmarska 2004, emend. |
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**** Class [[Mediophyceae]] Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004 |
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***** Subclass Chaetocerotophycidae Round & R.M. Crawford in Round et al. 1990, emend. |
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***** Subclass Lithodesmiophycidae Round & R.M. Crawford in Round et al. 1990, emend. |
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***** Subclass Thalassiosirophycidae Round & R.M. Crawford in Round et al. 1990 |
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***** Subclass Cymatosirophycidae Round & R.M. Crawford in Round et al. 1990 |
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***** Subclass Odontellophycidae D.G. Mann in Adl et al. 2019 |
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***** Subclass Chrysanthemodiscophycidae D.G. Mann in Adl et al. 2019 |
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**** Class [[Biddulphiophyceae]] D.G. Mann in Adl et al. 2019 |
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***** Subclass Biddulphiophycidae Round and R.M. Crawford in Round et al. 1990, emend. |
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***** Biddulphiophyceae incertae sedis (''[[Attheya]]'') |
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**** Class [[Bacillariophyceae]] Haeckel 1878, emend. |
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***** Bacillariophyceae incertae sedis (Striatellaceae) |
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***** Subclass Urneidophycidae Medlin 2016 |
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***** Subclass Fragilariophycidae Round in Round, Crawford & Mann 1990, emend. |
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***** Subclass Bacillariophycidae D.G. Mann in Round, Crawford & Mann 1990, emend. |
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See [[taxonomy of diatoms]] for more details. |
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==Gallery== |
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<gallery mode="packed" widths="200px" heights="160px" style="float:left" caption="Scanning electron microscope images"> |
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File:Surirella spiralis - SEM MUSE - sharpened.jpeg|Diatom ''Surirella spiralis'' |
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File:Diatoms-HCMR.jpg|Diatoms ''Thalassiosira'' sp. on a membrane filter, pore size 0.4 μm. |
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File:Paralia sulcata diatom.tif|Diatom ''Paralia sulcata''. |
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File:Achanthes trinodis - SEM MUSE.tiff|Diatom ''Achanthes trinodis'' |
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</gallery> |
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{{clear}} |
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<gallery mode="packed" style="float:left" heights="170px"> |
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File:Bacillaria paxillifera.jpg| Stand-alone cell of ''[[Bacillaria paxillifer]]'' |
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File:Bacillaria paxillifer.tif| Colonial group of ''Bacillaria paxillifer'' |
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</gallery> |
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{{ external media |
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| video1 = [https://www.youtube.com/watch?v=Nysdq_plUTg&ab_channel=JourneytotheMicrocosmos Bacillaria: Distractingly Beautiful Crystal Colonies] – Journey to the Microcosmos: |
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}} |
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{{clear}} |
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Three diatom species were sent to the [[International Space Station]], including the huge (6 mm length) diatoms of Antarctica and the exclusive colonial diatom, ''Bacillaria paradoxa''. The cells of ''Bacillaria'' moved next to each other in partial but opposite synchrony by a [[microfluidic]]s method.<ref>{{cite journal | last1=Mishra | first1=Meerambika | last2=Arukha | first2=Ananta P. | last3=Bashir | first3=Tufail | last4=Yadav | first4=Dhananjay | last5=Prasad | first5=G. B. K. S. | title=All New Faces of Diatoms: Potential Source of Nanomaterials and Beyond | journal=Frontiers in Microbiology | publisher=Frontiers Media SA | volume=8 | date=5 July 2017 | page=1239 | issn=1664-302X | doi=10.3389/fmicb.2017.01239| pmid=28725218 | pmc=5496942 | doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=16 October 2017 }}.</ref> |
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== Evolution and fossil record == |
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=== Origin === |
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Heterokont chloroplasts appear to derive from those of [[red algae]], rather than directly from [[prokaryote]]s as occurred in [[plant]]s. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record. |
Heterokont chloroplasts appear to derive from those of [[red algae]], rather than directly from [[prokaryote]]s as occurred in [[plant]]s. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record. |
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=== Earliest fossils === |
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The earliest known fossil diatoms date from the early [[Jurassic]] (~185 [[Mega-annum|Ma ago]]),<ref name=kooistra96>{{cite journal | last = Kooistra | first = W. H. C. F. | last2 = Medlin | first2 = L. K. | title = Evolution of the Diatoms (Bacillariophyta) IV A Reconstruction of Their Age from Small Subunit rRNA Coding Regions and the Fossil Record | journal = Molecular Phylogenetics and Evolution | volume = 6 | issue = 3 | pages = 391–407 | publisher = Academic Press | year = 1996 | url = http://www.ingentaconnect.com/content/ap/fy/1996/00000006/00000003/art00088 | accessdate = 2013-11-14 | doi = 10.1006/mpev.1996.0088 | pmid = 8975694}}</ref> although the [[molecular clock]]<ref name=kooistra96/> and [[sedimentary rock|sedimentary]]<ref name=schieber00>{{cite journal | last = Schieber | first = Jürgen | last2 = Krinsley | first2 = Dave | last3 = Riciputi | first3 = Lee | title = Diagenic origin of quartz silt in mudstones and implications for silica cycling | journal = Nature | volume = 406 | pages = 981–985 | publisher = Nature Publishing Group | year = 2000 | url = http://www.nature.com/nature/journal/v406/n6799/abs/406981a0.html | issn = 0028-0836 | doi = 10.1038/35023143 | pmid = 10984049| accessdate = 2013-11-14 | issue = 6799}}</ref> evidence suggests an earlier origin. It has been suggested that their origin may be related to the [[Permian–Triassic extinction event|end-Permian mass extinction]] (~250 Ma), after which many marine [[ecological niche|niche]]s were opened.<ref name=medlin97>{{cite journal | last1 = Medlin | first1 = L. K. | last2 = Kooistra | first2 = W. H. C. F. | last3 = Gersonde | first3 = R. | last4 = Sims | first4 = P. A. | last5 = Wellbrock | first5 = U. | year = 1997 | title = Is the origin of the diatoms related to the end-Permian mass extinction? | url = | journal = Nova Hedwegia | volume = 65 | issue = | pages = 1–11 }}</ref> The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was [[cryptic (zoology)|cryptic]].<ref name=raven04>{{cite journal | last1 = Raven | first1 = J. A. | last2 = Waite | first2 = A. M. | year = 2004 | title = The evolution of silicification in diatoms: inescapable sinking and sinking as escape? | url = http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-8137.2004.01022.x | journal = New Phytologist | volume = 162 | issue = | pages = 45–61 | doi=10.1111/j.1469-8137.2004.01022.x}}</ref> Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major deposits of fossil diatoms found as far back as the early [[Cretaceous]], and some rocks ([[diatomaceous earth]], diatomite, kieselguhr) being composed almost entirely of them. |
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The earliest known fossil diatoms date from the early [[Jurassic]] (~185 [[Mega-annum|Ma ago]]),<ref name="Kooistra 1996">{{cite journal |doi=10.1006/mpev.1996.0088 |pmid=8975694 |title=Evolution of the Diatoms (Bacillariophyta) |journal=Molecular Phylogenetics and Evolution |volume=6 |issue=3 |pages=391–407 |year=1996 |last1=Kooistra |first1=Wiebe H.C.F. |last2=Medlin |first2=Linda K. }}</ref> although the [[molecular clock]]<ref name="Kooistra 1996" /> and [[sedimentary rock|sedimentary]]<ref name="Schieber 2000">{{cite journal |doi=10.1038/35023143 |pmid=10984049 |year=2000 |last1=Schieber |first1=Jürgen |title=Diagenetic origin of quartz silt in mudstones and implications for silica cycling |journal=Nature |volume=406 |issue=6799 |pages=981–5 |last2=Krinsley |first2=Dave |last3=Riciputi |first3=Lee |bibcode=2000Natur.406..981S |s2cid=4417951 }}</ref> evidence suggests an earlier origin. It has been suggested that their origin may be related to the [[Permian–Triassic extinction event|end-Permian mass extinction]] (~250 Ma), after which many marine [[ecological niche|niches]] were opened.<ref name="Medlin 1997">{{cite journal |hdl=10013/epic.12689 | last1=Medlin | first1=L. K. | last2=Kooistra | first2=W. H. C. F. | last3=Gersonde | first3=R. | last4=Sims | first4=P. A. | last5=Wellbrock | first5=U. | year=1997 | title=Is the origin of the diatoms related to the end-Permian mass extinction? | journal=Nova Hedwigia | volume=65 | issue=1–4 | pages=1–11 | doi=10.1127/nova.hedwigia/65/1997/1 }}</ref> The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was [[cryptic (zoology)|cryptic]].<ref name="Raven 2004">{{cite journal |doi=10.1111/j.1469-8137.2004.01022.x |jstor=1514475 |title=The evolution of silicification in diatoms: Inescapable sinking and sinking as escape? |journal=New Phytologist |volume=162 |issue=1 |pages=45–61 |year=2004 |last1=Raven |first1=J. A. |last2=Waite |first2=A. M. |doi-access=free |bibcode=2004NewPh.162...45R }}</ref> Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early [[Cretaceous]], and with some rocks such as [[diatomaceous earth]], being composed almost entirely of them. |
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===Relation to grasslands === |
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Although the diatoms may have existed since the [[Triassic]], the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the [[Phanerozoic]] (before 544 Ma), it is believed that [[bacteria|microbial]] or [[inorganic]] processes weakly regulated the ocean's silicon cycle.<ref name="SchneiderBoston1993">{{cite book|author1= R. Siever|author2= Stephen Henry Schneider|author3= Penelope J. Boston|title= Scientists on Gaia|url= http://books.google.com/books?id=h83nGwAACAAJ|accessdate= 2013-11-14|date= January 1993|publisher= Mit Press|isbn= 978-0-262-69160-4|pages= 287–295|chapter= Silica in the oceans: biological-geological interplay}}</ref><ref>{{cite journal |last = Kidder | first = David L. | last2 = Erwin | title = Secular Distribution of Biogenic Silica through the Phanerozoic: Comparison of Silica-Replaced Fossils and Bedded Cherts at the Series Level | journal = The Journal of Geology | volume = 109 | issue = 4 | pages = 509–522 | publisher = The University of Chicago Press | year = 2001 | doi = 10.1086/320794 | jstor = 320794 | first2 = Douglas H. | bibcode= 2001JG....109..509K}}</ref><ref name=grenne03>{{cite journal | last1 = Grenne | first1 = T. | last2 = Slack | first2 = J. F. | year = 2003 | title = Paleozoic and Mesozoic silica-rich seawater: evidence from hematitic chert (jasper) deposits | url = http://geology.geoscienceworld.org/cgi/content/abstract/31/4/319 | journal = Geology | volume = 31 | issue = 4 | pages = 319–322 | bibcode = 2003Geo....31..319G | doi = 10.1130/0091-7613(2003)031<0319:PAMSRS>2.0.CO;2 | issn = 0091-7613 }}</ref> Subsequently, the cycle appears dominated (and more strongly regulated) by the [[radiolaria]]ns and [[sea sponge|siliceous sponges]], the former as [[zooplankton]], the latter as [[sedentary lifestyle|sedentary]] [[filter-feeder]]s primarily on the [[continental shelf|continental shelves]].<ref>{{cite journal | last = Racki | first = Grzegorz | last2 = Cordey | first2 = Fabrice | title = Radiolarian palaeocology and radiolarites: is the present the key to the past? | journal = Earth-Science Reviews | volume = 52 | issue = 1–3 | pages = 83–120 | publisher = Elsevier B. V. | year = 2000 | url = http://www.sciencedirect.com/science/article/pii/S0012825200000246 | accessdate = 2013-11-14 | doi = 10.1016/S0012-8252(00)00024-6 | bibcode= 2000ESRv...52...83R}}</ref> Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms. |
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The expansion of [[grassland]] [[biome]]s and the [[evolutionary radiation]] of [[grass]]es during the [[Miocene]] is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era.<ref>{{cite journal |doi=10.1126/science.1095964 |pmid=15256663 |title=The Evolution of Modern Eukaryotic Phytoplankton |journal=Science |volume=305 |issue=5682 |pages=354–60 |year=2004 |last1=Falkowski |first1=P. G. |last2=Katz |first2=Miriam E. |last3=Knoll |first3=Andrew H. |last4=Quigg |first4=Antonietta |last5=Raven |first5=John A. |last6=Schofield |first6=Oscar |last7=Taylor |first7=F. J. R. |bibcode=2004Sci...305..354F |citeseerx=10.1.1.598.7930 |s2cid=451773 }}</ref><ref>{{cite journal |doi=10.2110/palo.2003.p03-108 |jstor=27670327 |title=Impact of Grassland Radiation on the Nonmarine Silica Cycle and Miocene Diatomite |journal=PALAIOS |volume=20 |issue=2 |pages=198–206 |year=2005 |last1=Kidder |first1=D. L. |last2=Gierlowski-Kordesch |first2=E. H. |bibcode=2005Palai..20..198K |s2cid=140584104 }}</ref> Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.<ref name="Lazarus2014">{{cite journal |doi=10.1371/journal.pone.0084857 |pmid=24465441 |pmc=3898954 |title=Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change |journal=PLOS ONE |volume=9 |issue=1 |pages=e84857 |year=2014 |last1=Lazarus |first1=David |last2=Barron |first2=John |last3=Renaudie |first3=Johan |last4=Diver |first4=Patrick |last5=Türke |first5=Andreas |bibcode=2014PLoSO...984857L |doi-access=free }}</ref> |
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===Relation to climate === |
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However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves,<ref name=maldonado99>{{cite journal | last1 = Maldonado | first1 = M. | last2 = Carmona | first2 = M. C. | last3 = Uriz | first3 = J. M. | last4 = Cruzado | first4 = A. | year = 1999 | title = Decline in Mesozoic reef-building sponges explained by silicate limitation | url = http://www.nature.com/nature/journal/v401/n6755/abs/401785a0.html | journal = Nature | volume = 401 | issue = 6755| pages = 785–788 | doi= 10.1038/44560|bibcode = 1999Natur.401..785M }}</ref> suggests that this takeover began in the Cretaceous (146 Ma to 65 Ma), while evidence from radiolarians suggests "take-over" did not begin until the [[Cenozoic]] (65 Ma to present).<ref>{{cite journal | last = Harper | first = Howard E., Jr. | title = Silica, diatoms, and Cenozoic radiolarian evolution | journal = Geology | volume = 3 | issue = 4 | pages = 175 | publisher = The Geological Society of America | year = 1975 | url = http://mr.crossref.org/iPage?doi=10.1130%2F0091-7613%281975%293%3C175%3ASDACRE%3E2.0.CO%3B2 | doi = 10.1130/0091-7613(1975)3<175:SDACRE>2.0.CO;2 | accessdate = 2013-11-11 | issn = 0091-7613 | first2 = Andrew H.| last2 = Knoll |bibcode = 1975Geo.....3..175H }}</ref> The expansion of [[grassland]] [[biome]]s and the [[evolutionary radiation]] of [[grass]]es during the [[Miocene]] is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era.<ref>{{cite journal |last= Falkowski |first= P.G. |year= 2004 |title= The evolution of modern eukaryotic phytoplankton |journal= Science |volume= 305 |pages= 354–60 |doi= 10.1126/science.1095964 |pmid= 15256663 |issue= 5682 |bibcode = 2004Sci...305..354F |last3= Knoll |first3= Andrew H. |last4= Quigg |first4= Antonietta |last5= Raven |first5= John A. |last6= Schofield |first6= Oscar |last7= Taylor |first7= F. J. R. |display-authors= etal}}</ref><ref>{{cite journal |last= Kidder |first= D.L. |author2= Gierlowski-Kordesch, E.H. |year= 2005 |title= Impact of grassland radiation on the nonmarine silica cycle and Miocene diatomite |journal= PALAIOS |volume= 20 |pages= 198–206 |doi= 10.2110/palo.2003.p03-108 |issue= 2 }}</ref> Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.<ref name="Lazarus2014">{{cite journal |last= Lazarus |first= D.|year= 2014 |title= Cenozoic planktonic marine diatom diversity and correlation to climate change |journal= PLoS ONE |volume= 9 |pages= 1–18 |doi= 10.1371/journal.pone.0084857 |last3= Renaudie|first3= Johan|last4= Diver|first4= Patrick|last5= Türke|first5= Andreas|bibcode = 2014PLoSO...984857L |display-authors= etal}} {{open access}}</ref> Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios,<ref>IPCC Core Writing Team, 2007. Climate Change 2007: Synthesis Report. 104.</ref> could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.<ref name="Lazarus2014"/> |
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Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios,<ref>IPCC Core Writing Team, 2007. "Climate Change 2007: Synthesis Report". 104.</ref> could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.<ref name="Lazarus2014" /> |
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=== Method of investigation === |
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==Fossil record== |
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The fossil record of diatoms has largely been established through the recovery of their siliceous [[frustule]]s in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom [[biostratigraphy]], which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land.<ref name="Scherer 2007">{{cite journal |last1=Scherer |first1=R. P. |last2=Gladenkov |first2=A. Yu. |last3=Barron |first3=J. A. |year=2007 |title=Methods and applications of Cenozoic marine diatom biostratigraphy |journal=Paleontological Society Papers |volume=13 |pages=61–83 |doi=10.1017/S1089332600001467 }}</ref> Where diatom [[biozone]]s are well established and calibrated to the [[geomagnetic polarity time scale]] (e.g., [[Southern Ocean]], [[North Pacific]], eastern equatorial [[Pacific]]), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for [[Cenozoic]] diatom assemblages is several hundred thousand years. |
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[[File:Paralia sulcata diatom.tif|thumb|250px|''Paralia sulcata'' diatom imaged using the University of Tasmania scanning electron microscope.]] |
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The fossil record of diatoms has largely been established through the recovery of their siliceous [[frustule]]s in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom [[biostratigraphy]], which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land.<ref name=Scherer07>Scherer, R.P., Gladenkov, A.Yu., and Barron, J.A. (2007). Methods and applications of Cenozoic marine diatom biostratigraphy. "Paleontological Society Papers" '''13''', 61–83</ref> Where diatom [[biozone]]s are well established and calibrated to the [[geomagnetic polarity time scale]] (e.g., [[Southern Ocean]], [[North Pacific]], eastern equatorial [[Pacific]]), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for [[Cenozoic]] diatom assemblages is several hundred thousand years. |
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Diatoms preserved in lake sediments are widely used for [[Paleoecology|paleoenvironmental reconstructions]] of [[Quaternary]] climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity. |
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The [[Cretaceous]] record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The [[Cretaceous–Paleogene extinction event]], which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.<ref name=Harwood07>Harwood, D.M., Nikolaev, V.A., and Winter, D.M. (2007). Cretaceous record of diatom evolution, radiation, and expansion. "Paleontological Society Papers" '''13''', 33–59</ref> |
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[[File:Diatoms-HCMR.jpg|thumb|250x250px|Diatoms ''Chaetoceros'' spp. on a membrane filter (pore size 0.4 μm) imaged using the Hellenic Centre for Marine Research scanning electron microscope. Thermaikos Gulf, Greece, 2004.]] |
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Although no mass extinctions of marine diatoms have been observed during the [[Cenozoic]], times of relatively rapid evolutionary turnover in marine diatom assemblages occurred near the [[Paleocene]]–[[Eocene]] boundary<ref name=Strelnikova90>Strelnikova, N. I. (1990). Evolution of diatoms during the Cretaceous and Paleogene periods. In: Simola, H. (ed.), "Proceedings of the Tenth International Diatom Symposium", Koeltz Scientific Books, Koenigstein, Germany, pp. 195–204</ref> and at the [[Eocene]]–[[Oligocene]] boundary.<ref name=Baldauf93>Baldauf, J.G. (1993). Middle Eocene through early Miocene diatom floral turnover. In: Prothero D., Berggren, W.H., (eds.), "Eocene-Oligocene climatic and biotic evolution", Princeton University Press, Princeton, NJ, USA, pp 310–326</ref> Further turnover of assemblages took place at various times between the middle [[Miocene]] and late [[Pliocene]],<ref name=Barron03>Barron, J.A. (2003). Appearance and extinction of planktonic diatoms during the past 18 m.y. in the Pacific and Southern oceans. "Diatom Research" '''18''', 203–224</ref> in response to progressive cooling of polar regions and the development of more endemic diatom assemblages. A global trend toward more delicate diatom frustules has been noted from the [[Oligocene]] to the [[Quaternary]].<ref name="Scherer07"/> This coincides with an increasingly more vigorous circulation of the ocean’s surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major [[ice sheet]] expansion on [[Antarctica]] and progressive cooling through the [[Neogene]] and [[Quaternary]] towards a bipolar glaciated world. This drove the diatoms into uptaking silica more competitively (i.e., to use less silica in formation of their [[frustule]]s). Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic [[upwelling]]. |
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===Isotope records=== |
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==Collection== |
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[[File:Triceratium morlandii var. morlandii.jpg|thumb| {{center|Intricate silicate (glass) shell, 32-40 million years old, of a diatom [[microfossil]]}}]] |
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Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. ''[[Cladophora]]'' is frequently covered with ''[[Cocconeis]]'', an elliptically shaped diatom; ''Vaucheria'' is often covered with small forms. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. |
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{{further|microfossils}} |
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When diatoms die their shells ([[frustule]]s) can settle on the [[seafloor]] and become [[microfossil]]s. Over time, these microfossils become buried as [[opal]] deposits in the [[marine sediment]]. [[Paleoclimatology]] is the study of past climates. [[Proxy data]] is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. [[Paleoclimate proxies]] refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements.<ref>{{Cite web|title=What Are "Proxy" Data? {{!}} National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC)|url=https://www.ncdc.noaa.gov/news/what-are-proxy-data|access-date=2020-10-20|website=www.ncdc.noaa.gov|archive-date=8 March 2020|archive-url=https://web.archive.org/web/20200308170642/https://www.ncdc.noaa.gov/news/what-are-proxy-data|url-status=live}}</ref> An example of proxies is the use of diatom [[marine isotope stage|isotope records]] of [[δ13C]], [[δ18O]], [[Isotopes of silicon|δ30Si]] (δ13C<sub>diatom</sub>, δ18O<sub>diatom</sub>, and δ30Si<sub>diatom</sub>). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west [[Pacific Ocean]], including nutrient supply and the efficiency of the soft-tissue [[biological pump]], from the modern day back to [[Marine Isotope Stage 5#Marine Isotope Stage (MIS) 5e|marine isotope stage 5e]], which coincides with the [[Eemian|last interglacial period]]. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional [[halocline]] stratification and increased nutrient supply to the [[photic zone]].<ref name="Swann Snelling 2015">{{cite journal | last1=Swann | first1=G. E. A. | last2=Snelling | first2=A. M. | title=Photic zone changes in the north-west Pacific Ocean from MIS 4–5e | journal=Climate of the Past | publisher=Copernicus GmbH | volume=11 | issue=1 | date=2015-01-06 | issn=1814-9332 | doi=10.5194/cp-11-15-2015 | pages=15–25| bibcode=2015CliPa..11...15S | doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License] {{Webarchive|url=https://web.archive.org/web/20110223101209/http://creativecommons.org//licenses//by//3.0// |date=23 February 2011 }}.</ref> |
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The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. They can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated. |
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<gallery mode="packed" style="float:left" heights="220px"> |
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Since diatoms form an important part of the food of [[mollusc]]s, [[tunicate]]s, and [[fish]]es, the [[alimentary tract]]s of these animals often yield forms that are not easily secured in other ways. Marine diatoms can be collected by direct water sampling, though benthic forms can be secured by scraping [[barnacle]]s, [[oyster]] shells, and other shells. |
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File:Ocean changes from the last interglacial to the modern day A.png |
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File:Ocean changes from the last interglacial to the modern day B.png |
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</gallery> |
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{{clear}} |
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The initial development of the halocline and [[Stratification (water)|stratified water column]] has been attributed to the onset of major [[Würm glaciation|Northern Hemisphere glaciation]] at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and [[sea surface temperature]]s.<ref>{{cite journal | last1=Sigman | first1=Daniel M. | last2=Jaccard | first2=Samuel L. | last3=Haug | first3=Gerald H. | title=Polar ocean stratification in a cold climate | journal=Nature | publisher=Springer Science and Business Media LLC | volume=428 | issue=6978 | year=2004 | issn=0028-0836 | doi=10.1038/nature02357 | pages=59–63 | pmid=14999278 | bibcode=2004Natur.428...59S | s2cid=4329978 | url=https://gfzpublic.gfz-potsdam.de/pubman/item/item_230448 | access-date=15 December 2021 | archive-date=19 February 2022 | archive-url=https://web.archive.org/web/20220219150343/https://gfzpublic.gfz-potsdam.de/pubman/faces/ViewItemOverviewPage.jsp?itemId=item_230448 | url-status=live }}</ref><ref name="Haug etal 2005">{{cite journal | last1=Haug | first1=Gerald H. | last2=Ganopolski | first2=Andrey | last3=Sigman | first3=Daniel M. | last4=Rosell-Mele | first4=Antoni | last5=Swann | first5=George E. A. | last6=Tiedemann | first6=Ralf | last7=Jaccard | first7=Samuel L. | last8=Bollmann | first8=Jörg | last9=Maslin | first9=Mark A. | last10=Leng | first10=Melanie J. | last11=Eglinton | first11=Geoffrey | display-authors = 6 | title=North Pacific seasonality and the glaciation of North America 2.7 million years ago | journal=Nature | publisher=Springer Science and Business Media LLC | volume=433 | issue=7028 | year=2005 | issn=0028-0836 | doi=10.1038/nature03332 | pages=821–825 | pmid=15729332 | bibcode=2005Natur.433..821H | s2cid=24116155 | url=https://gfzpublic.gfz-potsdam.de/pubman/item/item_231798 | access-date=15 December 2021 | archive-date=19 February 2022 | archive-url=https://web.archive.org/web/20220219150343/https://gfzpublic.gfz-potsdam.de/pubman/faces/ViewItemOverviewPage.jsp?itemId=item_231798 | url-status=live }}</ref><ref>{{cite journal | last1=Swann | first1=George E. A. | last2=Maslin | first2=Mark A. | last3=Leng | first3=Melanie J. | last4=Sloane | first4=Hilary J. | last5=Haug | first5=Gerald H. | title=Diatom δ18O evidence for the development of the modern halocline system in the subarctic northwest Pacific at the onset of major Northern Hemisphere glaciation | journal=Paleoceanography | publisher=American Geophysical Union (AGU) | volume=21 | issue=1 | date=2006-02-24 | issn=0883-8305 | doi=10.1029/2005pa001147 | pages=n/a| bibcode=2006PalOc..21.1009S | url=http://eprints.nottingham.ac.uk/id/eprint/2009 | doi-access=free }}</ref><ref name="Nie etal 2008">{{cite journal | last1=Nie | first1=Junsheng | last2=King | first2=John | last3=Liu | first3=Zhengyu | last4=Clemens | first4=Steve | last5=Prell | first5=Warren | last6=Fang | first6=Xiaomin | title=Surface-water freshening: A cause for the onset of North Pacific stratification from 2.75 Ma onward? | journal=Global and Planetary Change | publisher=Elsevier BV | volume=64 | issue=1–2 | year=2008 | issn=0921-8181 | doi=10.1016/j.gloplacha.2008.08.003 | pages=49–52| bibcode=2008GPC....64...49N }}</ref> The decrease of [[abyssal]] water upwelling associated with this may have contributed to the establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma.<ref name="Haug etal 2005" /> While the halocline appears to have prevailed through the [[late Pliocene]] and [[Gelasian|early Quaternary]] [[glacial cycle|glacial–interglacial cycles]],<ref>{{cite journal | last=Swann | first=George E.A. | title=Salinity changes in the North West Pacific Ocean during the late Pliocene/early Quaternary from 2.73Ma to 2.52Ma | journal=Earth and Planetary Science Letters | publisher=Elsevier BV | volume=297 | issue=1–2 | year=2010 | issn=0012-821X | doi=10.1016/j.epsl.2010.06.035 | pages=332–338 | bibcode=2010E&PSL.297..332S | url=http://nora.nerc.ac.uk/id/eprint/11147/1/swann_et_al_2010.pdf | access-date=15 December 2021 | archive-date=19 July 2018 | archive-url=https://web.archive.org/web/20180719072730/http://nora.nerc.ac.uk/id/eprint/11147/1/swann_et_al_2010.pdf | url-status=live }}</ref> other studies have shown that the stratification boundary may have broken down in the [[late Quaternary]] at glacial terminations and during the early part of interglacials.<ref>{{cite journal | last1=Sarnthein | first1=M. | last2=Gebhardt | first2=H. | last3=Kiefer | first3=T. | last4=Kucera | first4=M. | last5=Cook | first5=M. | last6=Erlenkeuser | first6=H. | title=Mid Holocene origin of the sea-surface salinity low in the subarctic North Pacific | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=23 | issue=20–22 | year=2004 | issn=0277-3791 | doi=10.1016/j.quascirev.2004.08.008 | pages=2089–2099| bibcode=2004QSRv...23.2089S }}</ref><ref>{{cite journal | last1=Jaccard | first1=S.L. | last2=Galbraith | first2=E.D. | last3=Sigman | first3=D.M. | last4=Haug | first4=G.H. | title=A pervasive link between Antarctic ice core and subarctic Pacific sediment records over the past 800kyrs | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=29 | issue=1–2 | year=2010 | issn=0277-3791 | doi=10.1016/j.quascirev.2009.10.007 | pages=206–212| bibcode=2010QSRv...29..206J }}</ref><ref>{{cite journal | last1=Galbraith | first1=Eric D. | last2=Kienast | first2=Markus | last3=Jaccard | first3=Samuel L. | last4=Pedersen | first4=Thomas F. | last5=Brunelle | first5=Brigitte G. | last6=Sigman | first6=Daniel M. | last7=Kiefer | first7=Thorsten | title=Consistent relationship between global climate and surface nitrate utilization in the western subarctic Pacific throughout the last 500 ka | journal=Paleoceanography | publisher=American Geophysical Union (AGU) | volume=23 | issue=2 | date=2008-05-23 | issn=0883-8305 | doi=10.1029/2007pa001518 | pages=n/a | bibcode=2008PalOc..23.2212G | s2cid=4082469 | url=https://archimer.ifremer.fr/doc/00237/34840/33281.pdf | access-date=15 December 2021 | archive-date=15 July 2021 | archive-url=https://web.archive.org/web/20210715195452/https://archimer.ifremer.fr/doc/00237/34840/33281.pdf | url-status=live }}</ref><ref>{{cite journal | last1=Brunelle | first1=Brigitte G. | last2=Sigman | first2=Daniel M. | last3=Jaccard | first3=Samuel L. | last4=Keigwin | first4=Lloyd D. | last5=Plessen | first5=Birgit | last6=Schettler | first6=Georg | last7=Cook | first7=Mea S. | last8=Haug | first8=Gerald H. | title=Glacial/interglacial changes in nutrient supply and stratification in the western subarctic North Pacific since the penultimate glacial maximum | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=29 | issue=19–20 | year=2010 | issn=0277-3791 | doi=10.1016/j.quascirev.2010.03.010 | pages=2579–2590| bibcode=2010QSRv...29.2579B }}</ref><ref>{{cite journal | last1=Kohfeld | first1=Karen E. | last2=Chase | first2=Zanna | title=Controls on deglacial changes in biogenic fluxes in the North Pacific Ocean | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=30 | issue=23–24 | year=2011 | issn=0277-3791 | doi=10.1016/j.quascirev.2011.08.007 | pages=3350–3363| bibcode=2011QSRv...30.3350K }}</ref><ref name="Swann Snelling 2015" /> |
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This section uses text from ''Methods in Plant Histology''.<ref name=chamberlain1901>Chamberlain, C. J. (1901) ''Methods in Plant Histology'', University of Chicago Press, USA</ref> |
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===Diversification=== |
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==Expressed sequence tagging== |
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The [[Cretaceous]] record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The [[Cretaceous–Paleogene extinction event]], which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.<ref name="Harwood etal 2007">{{cite journal |last1=Harwood |first1=D. M. |last2=Nikolaev |first2=V. A. |last3=Winter |first3=D. M. |year=2007 |title=Cretaceous record of diatom evolution, radiation, and expansion |journal=Paleontological Society Papers |volume=13 |pages=33–59 |doi=10.1017/S1089332600001455 }}</ref> |
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The first insights into the properties of the ''[[Phaeodactylum tricornutum]]'' gene repertoire were described using 1,000 [[expressed sequence tag]]s (ESTs).<ref name=scala02>{{cite journal | last=Scala | first=S. | last2=Carels|first2= N.|last3= Falciatore|first3= A.|last4= Chiusano|first4= M.L.|last5= Bowler|first5= C. | title=Genome Properties of the Diatom Phaeodactylum tricornutum | journal=Plant Physiol. | volume=129 | issue=3 | pages=993–1002 |date=July 2002 | pmid=12114555 | pmc=166495 | doi=10.1104/pp.010713 | url=http://www.plantphysiol.org/cgi/content/full/129/3/993 }}</ref> Subsequently, the number of ESTs was extended to 12,000 and the diatom EST database was constructed for functional analyses.<ref name=maheswari05>{{cite journal | last1 = Maheswari | first1 = U. | last2 = Montsant | first2 = A. | last3 = Goll | first3 = J. | last4 = Krishnasamy | first4 = S. | last5 = Rajyashri | first5 = K.R. | last6 = Patell | first6 = V.M. | last7 = Bowler | first7 = C. | year = 2005 | title = The Diatom EST Database | url = http://nar.oxfordjournals.org/cgi/content/full/33/suppl_1/D344 | journal = Nucleic Acids Research | volume = 33 | issue = Database issue| pages = 344–347 | pmid = 15608213 | doi = 10.1093/nar/gki121 | pmc = 540075 }}</ref> These sequences have been used to make a comparative analysis between ''P. tricornutum'' and the putative complete proteomes from the [[green algae|green alga]] ''[[Chlamydomonas reinhardtii]]'', the [[red alga]] ''[[Cyanidioschyzon merolae]]'', and the diatom ''[[Thalassiosira pseudonana]]''.<ref name=montsant05>{{cite journal | last=Montsant |first=A. | last2=Jabbari|first2= K.|last3= Maheswari|first3= U. |last4= Bowler|first4= C. | title=Comparative Genomics of the Pennate Diatom Phaeodactylum tricornutum | journal=Plant Physiol. | volume=137 | issue=2 | pages=500–13 |date=February 2005 | pmid=15665249 | pmc=1065351 | doi=10.1104/pp.104.052829 }}</ref> The diatom EST database now consists of over 200,000 ESTs from ''P. tricornutum'' (16 libraries) and ''T. pseudonana'' (7 libraries) cells grown in a range of different conditions, many of which correspond to different abiotic stresses (available at http://www.biologie.ens.fr/diatomics/EST3/).<ref>Maheswari U, Mock T, Armbrust EV, Bowler C: Update of the Diatom EST Database: a new tool for digital transcriptomics. Nucleic Acids Res 2008.</ref> |
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===Turnover=== |
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==Genome sequencing== |
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Although no mass extinctions of marine diatoms have been observed during the [[Cenozoic]], times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the [[Paleocene]]–[[Eocene]] boundary,<ref name="Strelnikova 1990">{{cite book |last=Strelnikova |first=N. I. |year=1990 |chapter=Evolution of diatoms during the Cretaceous and Paleogene periods |editor-last=Simola |editor-first=H. |title=Proceedings of the Tenth International Diatom Symposium |publisher=Koeltz Scientific Books |location=Koenigstein |pages=195–204 |isbn=3-87429-307-6 }}</ref> and at the [[Eocene]]–[[Oligocene]] boundary.<ref name="Baldauf 1993">{{cite book |last=Baldauf |first=J. G. |year=1993 |contribution=Middle Eocene through early Miocene diatom floral turnover |editor-last=Prothero |editor-first=D. |editor2-last=Berggren |editor2-first=W. H. |title=Eocene-Oligocene climatic and biotic evolution |publisher=Princeton University Press |location=Princeton |pages=310–326 |isbn=0-691-02542-8 }}</ref> Further turnover of assemblages took place at various times between the middle [[Miocene]] and late [[Pliocene]],<ref name="Barron 2003">{{cite journal |last=Barron |first=J. A. |year=2003 |title=Appearance and extinction of planktonic diatoms during the past 18 m.y. in the Pacific and Southern oceans |journal=Diatom Research |volume=18 |pages=203–224 |doi=10.1080/0269249x.2003.9705588 |s2cid=84781882 }}</ref> in response to progressive cooling of polar regions and the development of more endemic diatom assemblages. |
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The entire [[genome]]s of the centric diatom, ''[[Thalassiosira pseudonana]]'' (32.4 Mb),<ref name=armbrust04>{{cite journal | last1 = Armbrust | first1 = E. V.| year = 2004 | title = The genome of the diatom ''Thalassiosira pseudonana'': ecology, evolution, and metabolism | url = http://www.sciencemag.org/cgi/content/abstract/306/5693/79 | journal = Science | volume = 306 | issue = 5693| pages = 79–86 | doi=10.1126/science.1101156 | pmid=15459382|bibcode = 2004Sci...306...79A | last2 = Berges | first2 = JA | last3 = Bowler | first3 = C | last4 = Green | first4 = BR | last5 = Martinez | first5 = D | last6 = Putnam | first6 = NH | last7 = Zhou | first7 = S | last8 = Allen | first8 = AE | last9 = Apt | first9 = KE | last10 = Bechner | first10 = M | last11 = Brzezinski | first11 = MA | last12 = Chaal | first12 = BK | last13 = Chiovitti | first13 = A | last14 = Davis | first14 = AK | last15 = Demarest | first15 = MS | last16 = Detter | first16 = JC | last17 = Glavina | first17 = T | last18 = Goodstein | first18 = D | last19 = Hadi | first19 = MZ | last20 = Hellsten | first20 = U | last21 = Hildebrand | first21 = M | last22 = Jenkins | first22 = BD | last23 = Jurka | first23 = J | last24 = Kapitonov | first24 = VV | last25 = Kröger | first25 = N | last26 = Lau | first26 = WW | last27 = Lane | first27 = TW | last28 = Larimer | first28 = FW | last29 = Lippmeier | first29 = JC | last30 = Lucas | first30 = S }}</ref> and the pennate diatom, ''[[Phaeodactylum tricornutum]]'' (27.4 Mb),<ref name=bowler08>{{cite journal | last=Bowler | first=C. | year=2008 | title=The Phaeodactylum genome reveals the evolutionary history of diatom genomes | journal=[[Nature (journal)|Nature]] | volume=456 | pages=239–244 | doi=10.1038/nature07410 | pmid=18923393 | issue=7219 |bibcode = 2008Natur.456..239B | last3=Badger | first3=J. H. | last4=Grimwood | first4=J | last5=Jabbari | first5=K | last6=Kuo | first6=A | last7=Maheswari | first7=U | last8=Martens | first8=C | last9=Maumus | first9=F | last10=Otillar | first10=R. P. | last11=Rayko | first11=E | last12=Salamov | first12=A | last13=Vandepoele | first13=K | last14=Beszteri | first14=B | last15=Gruber | first15=A | last16=Heijde | first16=M | last17=Katinka | first17=M | last18=Mock | first18=T | last19=Valentin | first19=K | last20=Verret | first20=F | last21=Berges | first21=J. A. | last22=Brownlee | first22=C | last23=Cadoret | first23=J. P. | last24=Chiovitti | first24=A | last25=Choi | first25=C. J. | last26=Coesel | first26=S | last27=De Martino | first27=A | last28=Detter | first28=J. C. | last29=Durkin | first29=C | last30=Falciatore | first30=A |display-authors=etal}}</ref> have been [[genome sequencing|sequenced]]. Comparisons of the two fully sequenced diatom genomes finds that the ''P. tricornutum'' genome includes fewer genes (10,402 opposed to 11,776) than ''T. pseudonana'' and no major synteny (gene order) could be detected between the two genomes. ''T. pseudonana'' genes show an average of ~1.52 introns per gene as opposed to 0.79 in ''P. tricornutum'', suggesting recent widespread intron gain in the centric diatom.<ref name=bowler08/><ref>{{cite journal | last1 = Roy | first1 = SW | last2 = Penny | first2 = D | date = Jul 2007 | title = A very high fraction of unique intron positions in the intron-rich diatom Thalassiosira pseudonana indicates widespread intron gain | url = | journal = Mol Biol Evol. | volume = 24 | issue = 7| pages = 1447–57 | doi = 10.1093/molbev/msm048 | pmid = 17350938 }}</ref> Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the Bacillariophyceae compared to other eukaryotic groups.<ref name=bowler08/> Comparative genomics also established that a specific class of [[transposable elements]], the Diatom Copia-like retrotransposons (or CoDis), has been significantly amplified in the ''P. tricornutum'' genome with respect to ''T. pseudonana'', constituting 5.8 and 1% of the respective genomes.<ref name=maumus09>{{cite journal | last=Maumus |first=F. |author2=Allen, A.E.|author3=Mhiri, C.|author4=Hu, H.|author5=Jabbari, K.|author6=Vardi, A.|author7=Grandbastien, M.A.|author8=Bowler, C. | title=Potential impact of stress activated retrotransposons on genome evolution in a marine diatom | journal=BMC Genomics | year=2009 | pmid=20028555 | pmc=2806351 | doi=10.1186/1471-2164-10-624 | volume=10 | pages=624}} {{open access}}</ref> |
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A global trend toward more delicate diatom frustules has been noted from the [[Oligocene]] to the [[Quaternary]].<ref name="Scherer 2007" /> This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major [[ice sheet]] expansion on [[Antarctica]] and progressive cooling through the [[Neogene]] and [[Quaternary]] towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic [[upwelling]]. |
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Importantly, diatom genomics brought much information about the extent and dynamics of the endosymbiotic gene transfer (EGT) process. Comparison of the ''T. pseudonana'' proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage. EGT towards diatom genomes can be illustrated by the fact that the ''T. pseudonana'' genome encodes six proteins which are most closely related to genes encoded by the ''[[Guillardia theta]]'' ([[cryptomonad]]) [[nucleomorph]] genome. Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus.<ref name="armbrust04"/> More recent phylogenomic analyses of diatom proteomes provided evidence for a prasinophyte-like endosymbiont in the common ancestor of [[chromalveolates]] as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other [[stramenopile]]s. Therefore, it was proposed that chromalveolates are the product of serial secondary endosymbiosis first with a green algae, followed by a second one with a red algae that conserved the genomic footprints of the previous but displaced the green plastid.<ref>{{cite journal | last1 = Moustafa | first1 = A | last2 = Beszteri | first2 = B | last3 = Maier | first3 = UG | last4 = Bowler | first4 = C | last5 = Valentin | first5 = K | last6 = Bhattacharya | first6 = D | year = 2009 | title = Genomic footprints of a cryptic plastid endosymbiosis in diatoms | url = | journal = Science | volume = 324 | issue = | pages = 1724–1726 | doi=10.1126/science.1172983|bibcode = 2009Sci...324.1724M | pmid=19556510}}</ref> However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under-sequenced lineages such as red algae. |
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==Genetics== |
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In addition to EGT, [[horizontal gene transfer]] (HGT) can occur independently of an endosymbiotic event. The publication of the ''P. tricornutum'' genome reported that at least 587 ''P. tricornutum'' genes appear to be most closely related to bacterial genes, accounting for more than 5% of the ''P. tricornutum'' proteome. About half of these are also found in the ''T. pseudonana'' genome, attesting their ancient incorporation in the diatom lineage.<ref name="bowler08"/> |
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[[File:Phaeodactylum tricornutum.png|thumb|210px| {{center|''[[Phaeodactylum tricornutum]]'' is widely used as a [[model organism]]}}]] |
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=== Expressed sequence tagging === |
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==Forensic research== |
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In 2002, the first insights into the properties of the ''[[Phaeodactylum tricornutum]]'' gene repertoire were described using 1,000 [[expressed sequence tag]]s (ESTs).<ref name="Scala 2002">{{cite journal |doi=10.1104/pp.010713 |pmid=12114555 |pmc=166495 |title=Genome Properties of the Diatom Phaeodactylum tricornutum |journal=Plant Physiology |volume=129 |issue=3 |pages=993–1002 |year=2002 |last1=Scala |first1=S. |last2=Carels |first2=N |last3=Falciatore |first3=A |last4=Chiusano |first4=M. L. |last5=Bowler |first5=C }}</ref> Subsequently, the number of ESTs was extended to 12,000 and the diatom EST database was constructed for functional analyses.<ref name="Maheswari 2005">{{cite journal |doi=10.1093/nar/gki121 |pmid=15608213 |pmc=540075 |title=The Diatom EST Database |journal=Nucleic Acids Research |volume=33 |issue=Database issue |pages=D344–7 |year=2004 |last1=Maheswari |first1=U. |last2=Montsant |first2=A |last3=Goll |first3=J |last4=Krishnasamy |first4=S |last5=Rajyashri |first5=K. R. |last6=Patell |first6=V. M. |last7=Bowler |first7=C. }}</ref> These sequences have been used to make a comparative analysis between ''P. tricornutum'' and the putative complete proteomes from the [[green algae|green alga]] ''[[Chlamydomonas reinhardtii]]'', the [[red alga]] ''[[Cyanidioschyzon merolae]]'', and the diatom ''[[Thalassiosira pseudonana]]''.<ref name="Montsant 2005">{{cite journal |doi=10.1104/pp.104.052829 |pmid=15665249 |pmc=1065351 |title=Comparative Genomics of the Pennate Diatom Phaeodactylum tricornutum |journal=Plant Physiology |volume=137 |issue=2 |pages=500–13 |year=2005 |last1=Montsant |first1=A. |last2=Jabbari |first2=K |last3=Maheswari |first3=U |last4=Bowler |first4=C }}</ref> The diatom EST database now consists of over 200,000 ESTs from ''P. tricornutum'' (16 libraries) and ''T. pseudonana'' (7 libraries) cells grown in a range of different conditions, many of which correspond to different abiotic stresses.<ref>{{cite journal |doi=10.1093/nar/gkn905 |pmid=19029140 |pmc=2686495 |title=Update of the Diatom EST Database: A new tool for digital transcriptomics |journal=Nucleic Acids Research |volume=37 |issue=Database issue |pages=D1001–5 |year=2009 |last1=Maheswari |first1=U. |last2=Mock |first2=T. |last3=Armbrust |first3=E. V. |last4=Bowler |first4=C. }}</ref> |
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The main goal of diatom analysis in [[forensic]]s is to differentiate a death by submersion from a post-mortem immersion of a body in water. Laboratory tests may reveal the presence of diatoms in the body. Since the silica-based skeletons of diatoms do not readily decay, they can sometimes be detected even in heavily decomposed bodies. As they do not occur naturally in the body, if laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good [[evidence]] of drowning as the [[cause of death]]. Further matching of [[diatoms]] from bone marrow and drowning site can strengthen this supportive evidence and a positive conclusion can be drawn whether a person was living or not when submerged.<ref>{{cite journal |last1=Verma |first1=K. |year=2013 |title=Role of Diatoms in the World of Forensic Science |journal=J. Forensic. Res. |volume=4 |issue= 2|pages= |publisher= |doi=10.4172/2157-7145.1000181 |url=http://www.omicsonline.org/2157-7145/2157-7145-4-181.php?aid=14679 |accessdate=5 September 2013}}</ref> |
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=== Genome sequencing === |
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==Nanotechnology research== |
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[[File:Thalassiosira pseudonana.jpg|thumb|210px| {{center|''[[Thalassiosira pseudonana]]'' was the first eukaryotic marine phytoplankton to have its genome sequenced}}]] |
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The deposition of silica by diatoms may also prove to be of utility to [[nanotechnology]].<ref name=bradbury04>{{cite journal | last1 = Bradbury | first1 = J. | year = 2004 | title = Nature's Nanotechnologists: Unveiling the Secrets of Diatoms | journal = PLoS Biology | volume = 2 | issue = 10| pages = 1512–1515 | doi = 10.1371/journal.pbio.0020306 | pmid=15486572 | pmc=521728}} {{open access}}</ref> Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems; [[semiconductor]] [[nanolithography]]; and even using diatom valves as vehicles for [[drug delivery]]. Using an appropriate [[artificial selection|artificial selection procedure]], diatoms that produce valves of particular shapes and sizes could be evolved in the laboratory, and then used in [[chemostat]] cultures to [[mass production|mass-produce]] nanoscale components.<ref name=drum03>{{cite journal | last=Drum | first=R.W. |author2=Gordon, R. | year=2003 | title=Star Trek replicators and diatom nanotechnology | journal=Trends Biotechnology | volume=21 | pages=325–328 | doi=10.1016/S0167-7799(03)00169-0 | url=http://www.cell.com/trends/biotechnology/abstract/S0167-7799(03)00169-0?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0167779903001690%3Fshowall%3Dtrue&cc=y=}}</ref> It has also been proposed that diatoms could be used as a component of solar cells, by substituting [[Photosensitivity|photosensitive]] [[titanium dioxide]] for the silicon dioxide normally used in the creation of cell walls.<ref>{{cite web | url=http://www.eetimes.com/showArticle.jhtml?articleID=216500176 | title=Diatoms could triple solar cell efficiency | last=Johnson | first=R.C. | date=9 April 2009 | accessdate=13 April 2009 | publisher=[[EE Times]] }}</ref> Diatom biofuel producing solar panels have also been proposed.<ref>Ramachandra, T.V., D.M. Mahapatra, Karthick B. & R. Gordon [http://pubs.acs.org/doi/abs/10.1021/ie900044j Milking diatoms for sustainable energy: biochemical engineering versus gasoline-secreting diatom solar panels] Industrial & Engineering Chemistry Research 48(19, Complex Materials II special issue, October), 8769-8788 2009</ref> |
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In 2004, the entire [[genome]] of the centric diatom, ''[[Thalassiosira pseudonana]]'' (32.4 Mb) was sequenced,<ref name="Armbrust 2004">{{cite journal |doi=10.1126/science.1101156 |pmid=15459382 |title=The Genome of the Diatom Thalassiosira Pseudonana: Ecology, Evolution, and Metabolism |journal=Science |volume=306 |issue=5693 |pages=79–86 |year=2004 |last1=Armbrust |first1=E. V. |last2=Berges |first2=John A. |last3=Bowler |first3=Chris |last4=Green |first4=Beverley R. |last5=Martinez |first5=Diego |last6=Putnam |first6=Nicholas H. |last7=Zhou |first7=Shiguo |last8=Allen |first8=Andrew E. |last9=Apt |first9=Kirk E. |last10=Bechner |first10=Michael |last11=Brzezinski |first11=Mark A. |last12=Chaal |first12=Balbir K. |last13=Chiovitti |first13=Anthony |last14=Davis |first14=Aubrey K. |last15=Demarest |first15=Mark S. |last16=Detter |first16=J. Chris |last17=Glavina |first17=Tijana |last18=Goodstein |first18=David |last19=Hadi |first19=Masood Z. |last20=Hellsten |first20=Uffe |last21=Hildebrand |first21=Mark |last22=Jenkins |first22=Bethany D. |last23=Jurka |first23=Jerzy |last24=Kapitonov |first24=Vladimir V. |last25=Kröger |first25=Nils |last26=Lau |first26=Winnie W. Y. |last27=Lane |first27=Todd W. |last28=Larimer |first28=Frank W. |last29=Lippmeier |first29=J. Casey |last30=Lucas |first30=Susan | display-authors = 6 | bibcode=2004Sci...306...79A |citeseerx=10.1.1.690.4884 |s2cid=8593895 }}</ref> followed in 2008 with the sequencing of the pennate diatom, ''[[Phaeodactylum tricornutum]]'' (27.4 Mb).<ref name="Bowler 2008">{{cite journal |doi=10.1038/nature07410 |pmid=18923393 |title=The Phaeodactylum genome reveals the evolutionary history of diatom genomes |journal=Nature |volume=456 |issue=7219 |pages=239–244 |year=2008 |last1=Bowler |first1=Chris |last2=Allen |first2=Andrew E. |last3=Badger |first3=Jonathan H. |last4=Grimwood |first4=Jane |last5=Jabbari |first5=Kamel |last6=Kuo |first6=Alan |last7=Maheswari |first7=Uma |last8=Martens |first8=Cindy |last9=Maumus |first9=Florian |last10=Otillar |first10=Robert P. |last11=Rayko |first11=Edda |last12=Salamov |first12=Asaf |last13=Vandepoele |first13=Klaas |last14=Beszteri |first14=Bank |last15=Gruber |first15=Ansgar |last16=Heijde |first16=Marc |last17=Katinka |first17=Michael |last18=Mock |first18=Thomas |last19=Valentin |first19=Klaus |last20=Verret |first20=Fréderic |last21=Berges |first21=John A. |last22=Brownlee |first22=Colin |last23=Cadoret |first23=Jean-Paul |last24=Chiovitti |first24=Anthony |last25=Choi |first25=Chang Jae |last26=Coesel |first26=Sacha |last27=De Martino |first27=Alessandra |last28=Detter |first28=J. Chris |last29=Durkin |first29=Colleen |last30=Falciatore |first30=Angela |display-authors = 6 | bibcode=2008Natur.456..239B |s2cid=4415177 |doi-access=free }}</ref> Comparisons of the two reveal that the ''P. tricornutum'' genome includes fewer genes (10,402 opposed to 11,776) than ''T. pseudonana''; no major synteny (gene order) could be detected between the two genomes. ''T. pseudonana'' genes show an average of ~1.52 introns per gene as opposed to 0.79 in ''P. tricornutum'', suggesting recent widespread intron gain in the centric diatom.<ref name="Bowler 2008" /><ref>{{cite journal |doi=10.1093/molbev/msm048 |pmid=17350938 |title=A Very High Fraction of Unique Intron Positions in the Intron-Rich Diatom Thalassiosira pseudonana Indicates Widespread Intron Gain |journal=Molecular Biology and Evolution |volume=24 |issue=7 |pages=1447–57 |year=2007 |last1=Roy |first1=S. W. |last2=Penny |first2=D. |doi-access=free }}</ref> Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the [[Bacillariophyceae]] compared to other [[eukaryotic]] groups.<ref name="Bowler 2008" /> [[Comparative genomics]] also established that a specific class of [[transposable elements]], the Diatom Copia-like retrotransposons (or CoDis), has been significantly amplified in the ''P. tricornutum'' genome with respect to ''T. pseudonana'', constituting 5.8 and 1% of the respective genomes.<ref name="Maumus etal 2009">{{cite journal |doi=10.1186/1471-2164-10-624 |pmid=20028555 |pmc=2806351 |title=Potential impact of stress activated retrotransposons on genome evolution in a marine diatom |journal=BMC Genomics |volume=10 |pages=624 |year=2009 |last1=Maumus |first1=Florian |last2=Allen |first2=Andrew E |last3=Mhiri |first3=Corinne |last4=Hu |first4=Hanhua |last5=Jabbari |first5=Kamel |last6=Vardi |first6=Assaf |last7=Grandbastien |first7=Marie-Angèle |last8=Bowler |first8=Chris |doi-access=free }}</ref> |
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== Microbial degradation == |
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===Endosymbiotic gene transfer=== |
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Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using [[hydrolytic]] enzymes to break down the organic algal material.<ref>{{cite journal|url=http://www.nature.com/nature/journal/v397/n6719/abs/397508a0.html|title=Accelerated dissolution of diatom silica by marine bacterial assemblages|author1=Kay D. Bidle|author2=Farooq Azam|journal=Nature|year=1999|volume=397|pages=508–512|issue=6719|doi=10.1038/17351|bibcode = 1999Natur.397..508B }}</ref><ref>{{cite journal|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0059977|title=The Structure of Microbial Community and Degradation of Diatoms in the Deep Near-Bottom Layer of Lake Baikal|year=2013 | doi=10.1371/journal.pone.0059977|volume=8|journal=PLoS ONE|pages=e59977|bibcode = 2013PLoSO...859977Z }} {{open access}}</ref> |
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Diatom genomics brought much information about the extent and dynamics of the endosymbiotic [[gene transfer]] (EGT) process. Comparison of the ''T. pseudonana'' proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage. EGT towards diatom genomes can be illustrated by the fact that the ''T. pseudonana'' genome encodes six proteins which are most closely related to genes encoded by the ''[[Guillardia theta]]'' ([[cryptomonad]]) [[nucleomorph]] genome. Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus.<ref name="Armbrust 2004" /> More recent [[phylogenomics|phylogenomic analyses]] of diatom proteomes provided evidence for a [[prasinophyte]]-like endosymbiont in the common ancestor of [[chromalveolates]] as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other [[stramenopile]]s. Therefore, it was proposed that chromalveolates are the product of serial secondary [[endosymbiosis]] first with a [[green algae]], followed by a second one with a [[red algae]] that conserved the genomic footprints of the previous but displaced the green plastid.<ref>{{cite journal |doi=10.1126/science.1172983 |pmid=19556510 |title=Genomic Footprints of a Cryptic Plastid Endosymbiosis in Diatoms |journal=Science |volume=324 |issue=5935 |pages=1724–6 |year=2009 |last1=Moustafa |first1=A. |last2=Beszteri |first2=B. |last3=Maier |first3=U. G. |last4=Bowler |first4=C. |last5=Valentin |first5=K. |last6=Bhattacharya |first6=D. |bibcode=2009Sci...324.1724M |s2cid=11408339 |url=http://epic.awi.de/20816/1/Mou2009a.pdf |access-date=13 January 2019 |archive-url=https://web.archive.org/web/20140421015051/http://epic.awi.de/20816/1/Mou2009a.pdf |archive-date=21 April 2014 |url-status=dead }}</ref> However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under-sequenced lineages such as red algae. |
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===Horizontal gene transfer=== |
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In addition to EGT, [[horizontal gene transfer]] (HGT) can occur independently of an endosymbiotic event. The publication of the ''P. tricornutum'' genome reported that at least 587 ''P. tricornutum'' genes appear to be most closely related to bacterial genes, accounting for more than 5% of the ''P. tricornutum'' proteome. About half of these are also found in the ''T. pseudonana'' genome, attesting their ancient incorporation in the diatom lineage.<ref name="Bowler 2008" /> |
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===Genetic engineering=== |
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To understand the biological mechanisms which underlie the great importance of diatoms in geochemical cycles, scientists have used the ''[[Phaeodactylum tricornutum]]'' and ''[[Thalassiosira]] spp.'' species as model organisms since the 90's.<ref name="genome-editing">{{cite journal |display-authors=2 |last1=Kroth |first1=Peter G. |last2=Bones |first2=Atle M. |last3=Daboussi |first3=Fayza |title=Genome editing in diatoms: achievements and goals |journal=Plant Cell Reports |date=Oct 2018 |volume=37 |issue=10 |pages=1401–1408 |doi=10.1007/s00299-018-2334-1 |pmid=30167805 |s2cid=52133809 |url=http://nbn-resolving.de/urn:nbn:de:bsz:352-2-1lxrzq3xck4wo8 |access-date=20 May 2021 |archive-date=19 February 2022 |archive-url=https://web.archive.org/web/20220219150345/https://kops.uni-konstanz.de/handle/123456789/44586 |url-status=live |hdl=11250/2590892 |hdl-access=free }}</ref> |
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Few molecular biology tools are currently available to generate mutants or transgenic lines : [[plasmids]] containing transgenes are inserted into the cells using the [[biolistic]] method<ref name="biolistic">{{cite journal |display-authors=2 |last1=Falciatore |first1=Angela |last2=Casotti |first2=Raffaella |last3=Leblanc |first3=Catherine |last4=Abrascia |first4=Chiara |last5=Bowler |first5=Chris |title=Transformation of Nonselectablporter Genes in Marine Diatomse Re |journal=Marine Biotechnology |date=May 2015 |volume=1 |issue=3 |pages=239–251 |doi=10.1007/PL00011773|pmid=10383998 |s2cid=22267097 }}</ref> or transkingdom [[bacterial conjugation]]<ref name="conjugation">{{cite journal |last1=Karas |first1=Bogumil J. |last2=Diner |first2=Rachel E. |last3=Lefebvre |first3=Stephane C. |last4=McQuaid |first4=Jeff |last5=Phillips |first5=Alex P. R. |last6=Noddings |first6=Chari M. |last7=Brunson |first7=John K. |last8=Valas |first8=Ruben E. |last9=Deerinck |first9=Thomas J. |last10=Jablanovic |first10=Jelena |last11=Gillard |first11=Jeroen T. F. |last12=Beeri |first12=Karen |last13=Ellisman |first13=Mark H. |last14=Glass |first14=John I. |last15=Hutchison Iii |first15=Clyde A. |last16=Smith |first16=Hamilton O. |last17=Venter |first17=J. Craig |last18=Allen |first18=Andrew E. |last19=Dupont |first19=Christopher L. |last20=Weyman |first20=Philip D. | display-authors = 6 | title=Designer diatom episomes delivered by bacterial conjugation |journal=Nature Communications |date=21 April 2015 |volume=6 |issue=1 |page=6925 |doi=10.1038/ncomms7925 |pmid=25897682 |pmc=4411287 |bibcode=2015NatCo...6.6925K |language=en |issn=2041-1723|doi-access=free }}</ref> (with 10<sup>−6</sup> and 10<sup>−4</sup> yield respectively<ref name="biolistic" /><ref name="conjugation" />), and other classical transfection methods such as [[electroporation]] or use of [[Polyethylene glycol|PEG]] have been reported to provide results with lower efficiencies.<ref name="conjugation" /> |
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Transfected plasmids can be either randomly integrated into the diatom's chromosomes or maintained as stable circular [[episomes]] (thanks to the CEN6-ARSH4-HIS3 yeast centromeric sequence<ref name="conjugation" />). The phleomycin/[[Zeocin|zeocin resistance gene Sh Ble]] is commonly used as a selection marker,<ref name="genome-editing" /><ref name="slattery">{{cite journal |last1=Slattery |first1=Samuel S. |last2=Diamond |first2=Andrew |last3=Wang |first3=Helen |last4=Therrien |first4=Jasmine A. |last5=Lant |first5=Jeremy T. |last6=Jazey |first6=Teah |last7=Lee |first7=Kyle |last8=Klassen |first8=Zachary |last9=Desgagné-Penix |first9=Isabel |last10=Karas |first10=Bogumil J. |last11=Edgell |first11=David R. | display-authors = 6 | title=An Expanded Plasmid-Based Genetic Toolbox Enables Cas9 Genome Editing and Stable Maintenance of Synthetic Pathways in Phaeodactylum tricornutum |journal=ACS Synthetic Biology |date=16 February 2018 |volume=7 |issue=2 |pages=328–338 |doi=10.1021/acssynbio.7b00191|pmid=29298053 }}</ref> and various transgenes have been successfully introduced and expressed in diatoms with stable transmissions through generations,<ref name="conjugation" /><ref name="slattery" /> or with the possibility to remove it.<ref name="slattery" /> |
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Furthermore, these systems now allow the use of the [[CRISPR gene editing|CRISPR-Cas genome edition tool]], leading to a fast production of functional [[Gene knockout|knock-out mutants]]<ref name="slattery" /><ref name="CRISPR">{{cite journal |display-authors=2 |last1=Nymark |first1=Marianne |last2=Sharma |first2=Amit Kumar |last3=Sparstad |first3=Torfinn |last4=Bones |first4=Atle M. |last5=Winge |first5=Per |title=A CRISPR/Cas9 system adapted for gene editing in marine algae |journal=Scientific Reports |date=July 2016 |volume=6 |issue=1 |pages=24951 |doi=10.1038/srep24951|pmid=27108533 |pmc=4842962 |bibcode=2016NatSR...624951N |doi-access=free }}</ref> and a more accurate comprehension of the diatoms' cellular processes. |
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==Human uses== |
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<gallery mode="packed" style="float:right" heights="200px"> |
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File:Diatomaceous Earth BrightField.jpg| [[Diatomaceous earth]] consisting of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms suspended in water.<br /><small>(click 3 times to fully enlarge)</small> |
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</gallery> |
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===Paleontology=== |
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Decomposition and decay of diatoms leads to [[organic matter|organic]] and [[inorganic]] (in the form of [[silicate]]s) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or [[bay mud]]s, since the inorganic matter is embedded in deposition of [[clay]]s and [[silt]]s and forms a permanent geological record of such marine strata (see [[siliceous ooze]]). |
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===Industrial=== |
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Diatoms, and their shells (frustules) as [[diatomite]] or [[diatomaceous earth]], are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology.<ref>{{cite journal| pmc=5496942 | pmid=28725218 | doi=10.3389/fmicb.2017.01239 | volume=8 | title=All New Faces of Diatoms: Potential Source of Nanomaterials and Beyond | year=2017 | journal=Front Microbiol | page=1239 | last1=Mishra | first1=M | last2=Arukha | first2=AP | last3=Bashir | first3=T | last4=Yadav | first4=D | last5=Gbks | first5=Prasad| doi-access=free }}</ref> |
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Diatomite is considered to be a natural nano material and has many uses and applications such as: production of various ceramic products, construction ceramics, refractory ceramics, special oxide ceramics, for production of humidity control materials, used as filtration material, material in the cement production industry, initial material for production of prolonged-release drug carriers, absorption material in an industrial scale, production of porous ceramics, glass industry, used as catalyst support, as a filler in plastics and paints, purification of industrial waters, pesticide holder, as well as for improving the physical and chemical characteristics of certain soils, and other uses.<ref>{{cite journal |last1=Reka |first1=Arianit A. |last2=Pavlovski |first2=Blagoj |last3=Makreski |first3=Petre |title=New optimized method for low-temperature hydrothermal production of porous ceramics using diatomaceous earth |journal=Ceramics International |date=October 2017 |volume=43 |issue=15 |pages=12572–12578 |doi=10.1016/j.ceramint.2017.06.132 |url=https://www.researchgate.net/publication/317746441 |access-date=8 April 2020 |archive-date=19 February 2022 |archive-url=https://web.archive.org/web/20220219150340/https://www.researchgate.net/publication/317746441_New_optimized_method_for_low-temperature_hydrothermal_production_of_porous_ceramics_using_diatomaceous_earth |url-status=live }}</ref><ref>{{cite journal |last1=Reka |first1=Arianit |last2=Anovski |first2=Todor |last3=Bogoevski |first3=Slobodan |last4=Pavlovski |first4=Blagoj |last5=Boškovski |first5=Boško |title=Physical-chemical and mineralogical-petrographic examinations of diatomite from deposit near village of Rožden, Republic of Macedonia |journal=Geologica Macedonica |date=29 December 2014 |volume=28 |issue=2 |pages=121–126 |url=http://js.ugd.edu.mk/index.php/GEOLMAC/article/view/920 |language=en |issn=1857-8586 |access-date=8 April 2020 |archive-url=https://web.archive.org/web/20200418184959/http://js.ugd.edu.mk/index.php/GEOLMAC/article/view/920 |archive-date=18 April 2020 |url-status=dead }}</ref><ref>{{cite journal |last1=Reka |first1=Arianit A. |last2=Pavlovski |first2=Blagoj |last3=Ademi |first3=Egzon |last4=Jashari |first4=Ahmed |last5=Boev |first5=Blazo |last6=Boev |first6=Ivan |last7=Makreski |first7=Petre |title=Effect Of Thermal Treatment Of Trepel At Temperature Range 800-1200˚C |journal=Open Chemistry |date=31 December 2019 |volume=17 |issue=1 |pages=1235–1243 |doi=10.1515/chem-2019-0132 |doi-access=free }}</ref> |
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Diatoms are also used to help determine the origin of materials containing them, including seawater. |
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=== Nanotechnology === |
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The deposition of silica by diatoms may also prove to be of utility to [[nanotechnology]].<ref name="Bradbury 2004">{{cite journal | last1=Bradbury | first1=J. | year=2004 | title=Nature's Nanotechnologists: Unveiling the Secrets of Diatoms | journal=PLOS Biology | volume=2 | issue=10| pages=1512–1515 | doi=10.1371/journal.pbio.0020306 | pmid=15486572 | pmc=521728 | doi-access=free }} {{open access}}</ref> Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems; [[semiconductor]] [[nanolithography]]; and even vehicles for [[drug delivery]]. With an appropriate [[artificial selection]] procedure, diatoms that produce valves of particular shapes and sizes might be evolved for cultivation in [[chemostat]] cultures to [[mass production|mass-produce]] nanoscale components.<ref name="Drum Gordon 2003">{{cite journal |doi=10.1016/S0167-7799(03)00169-0 |pmid=12902165 |title=Star Trek replicators and diatom nanotechnology |journal=Trends in Biotechnology |volume=21 |issue=8 |pages=325–8 |year=2003 |last1=Drum |first1=Ryan W. |last2=Gordon |first2=Richard }}</ref> It has also been proposed that diatoms could be used as a component of solar cells by substituting [[Photosensitivity|photosensitive]] [[titanium dioxide]] for the silicon dioxide that diatoms normally use to create their cell walls.<ref>{{cite magazine | url=http://www.eetimes.com/showArticle.jhtml?articleID=216500176 | archive-url=https://archive.today/20120731133532/http://www.eetimes.com/showArticle.jhtml?articleID=216500176 | url-status=dead | archive-date=31 July 2012 | title=Diatoms could triple solar cell efficiency | last=Johnson | first=R.C. | date=9 April 2009 | access-date=13 April 2009 | magazine=[[EE Times]] }}</ref> Diatom biofuel producing solar panels have also been proposed.<ref>{{cite journal |doi=10.1021/ie900044j |title=Milking Diatoms for Sustainable Energy: Biochemical Engineering versus Gasoline-Secreting Diatom Solar Panels |journal=Industrial & Engineering Chemistry Research |volume=48 |issue=19 |pages=8769–88 |year=2009 |last1=Ramachandra |first1=T. V. |last2=Mahapatra |first2=Durga Madhab |last3=b |first3=Karthick |last4=Gordon |first4=Richard }}</ref> |
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{{clear}} |
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<gallery mode="packed" style="float:left" heights="360px" caption="Supporting and regulating services provided by marine diatoms and some of their negative impacts"> |
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File:Supporting and regulating services provided by marine diatoms.png|alt=CNN = cloud condensation nuclei, DMS = dimethylsulphide, DMSP = dimethylsulfoniopropionate, VOCs = volatile organic compounds, dashed arrow: negative effect, solid arrow: positive effects| <small>{{space|40}} CNN = [[cloud condensation nuclei]], DMS = [[dimethylsulphide]], DMSP = [[dimethylsulfoniopropionate]], VOCs = [[volatile organic compound]]s<br />{{space|50}}dashed arrow: negative effect, solid arrow: positive effects</small> |
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</gallery> |
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{{clear}} |
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=== Forensic === |
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The main goal of diatom analysis in [[forensic]]s is to differentiate a death by submersion from a post-mortem immersion of a body in water. Laboratory tests may reveal the presence of diatoms in the body. Since the silica-based skeletons of diatoms do not readily decay, they can sometimes be detected even in heavily decomposed bodies. As they do not occur naturally in the body, if laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good [[evidence]] of drowning as the [[cause of death]]. The blend of diatom species found in a corpse may be the same or different from the surrounding water, indicating whether the victim drowned in the same site in which the body was found.<ref>{{cite journal |doi=10.1097/00000433-199109000-00009 |pmid=1750392 |title=Qualitative Diatom Analysis as a Tool to Diagnose Drowning |journal=The American Journal of Forensic Medicine and Pathology |volume=12 |issue=3 |pages=213–8 |year=1991 |last1=Auer |first1=Antti |s2cid=38370984 }}</ref> |
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==History of discovery== |
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[[File:Ränivetikas Tabellaria fenestrata.jpg|thumb| ''[[Tabellaria]]'' is a genus of freshwater diatoms, cuboid in shape with frustules (siliceous cell walls) attached at the corners so the colonies assume a zigzag shape.]] |
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The first illustrations of diatoms are found in an article from 1703 in Transactions of the Royal Society showing unmistakable drawings of ''Tabellaria''.<ref name="Pierella Karlusich etal 2020">{{Cite journal|last1=Pierella Karlusich|first1=Juan José|last2=Ibarbalz|first2=Federico M|last3=Bowler|first3=Chris|title=Exploration of marine phytoplankton: from their historical appreciation to the omics era|journal=Journal of Plankton Research|year=2020|volume=42|pages=595–612|doi=10.1093/plankt/fbaa049|doi-access=free|hdl=11336/143676|hdl-access=free}}</ref> Although the publication was authored by an unnamed English gentleman, there is recent evidence that he was Charles King of Staffordshire.<ref name="Pierella Karlusich etal 2020" /><ref>{{Cite journal|date=2019-08-01|title=Unmasking "The Eldest Son of The Father of Protozoology": Charles King|journal=Protist|language=en|volume=170|issue=4|pages=374–384|doi=10.1016/j.protis.2019.07.002|issn=1434-4610|last1=Dolan|first1=John R.|pmid=31479910|s2cid=201207778|doi-access=free}}</ref> It is only 80 years later that we find the first formally identified diatom, the colonial ''Bacillaria paxillifera'', discovered and described in 1783 by Danish naturalist [[Otto Friedrich Müller]].<ref name="Pierella Karlusich etal 2020" /> Like many others after him, he wrongly thought that it was an animal due to its ability to move. Even [[Charles Darwin]] saw diatom remains in dust whilst in the Cape Verde Islands, although he was not sure what they were. It was only later that they were identified for him as siliceous polygastrics. The infusoria that Darwin later noted in the face paint of Fueguinos, native inhabitants of Tierra del Fuego in the southern end of South America, were later identified in the same way. During his lifetime, the siliceous polygastrics were clarified as belonging to the ''Diatomaceae'', and Darwin struggled to understand the reasons underpinning their beauty. He exchanged opinions with the noted cryptogamist G. H. K. Thwaites on the topic. In the fourth edition of On the Origin of Species he stated that "''Few objects are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the high powers of the microscope''"? and reasoned that their exquisite morphologies must have functional underpinnings rather than having been created purely for humans to admire.<ref>{{Cite book|last=Darwin|first=Richard|title=On the Origin of Species by Means of Natural Selection: Or the Preservation of Favoured Races in the Struggle for Life|year=1866}}</ref> |
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{{clear}} |
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==See also== |
==See also== |
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<!-- Please respect alphabetical order --> |
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* [[Algae]] |
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*[[Highly branched isoprenoid]], long-chain [[alkene]]s produced by a small number of marine diatoms |
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* [[Biological pump]] |
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* [[Diatomaceous earth]] |
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== Notes == |
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* [[Phytoplankton]] |
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{{notelist}} |
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* [[Plankton]] |
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==References== |
==References== |
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{{ |
{{Reflist}} |
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==External links== |
== External links == |
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{{ |
{{Wikispecies | Bacillariophyta | Diatoms}} |
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{{Commons category|Diatoms}} |
{{Commons category|Diatoms}} |
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* [http://research.calacademy.org/research/diatoms/names/ Catalogue of Diatom Names, California Academy of Sciences] |
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* [http:// |
* [http://www.biologie.ens.fr/diatomics/EST/ Diatom EST database], {{lang|fr|[[École Normale Supérieure]]|italic=no}} |
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* [http://planktonnet.awi.de/ Plankton*Net], [[Taxonomy (biology)|taxonomic]] database including images of diatom species |
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* [http://www.biologie.ens.fr/diatomics/EST/ Diatom EST database], [[École Normale Supérieure]] |
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* [http://planktonnet.awi.de Plankton*Net], [[Taxonomy (biology)|taxonomic]] database including images of diatom species |
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* [http://www.ucmp.berkeley.edu/chromista/diatoms/diatomlh.html Life History and Ecology of Diatoms], [[University of California Museum of Paleontology]] |
* [http://www.ucmp.berkeley.edu/chromista/diatoms/diatomlh.html Life History and Ecology of Diatoms], [[University of California Museum of Paleontology]] |
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* [https://web.archive.org/web/20070209042756/http://hjs.geol.uib.no/Diatoms/index.html-ssi Diatoms: 'Nature's Marbles'], Eureka site, [[University of Bergen]] |
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* [http://cabinetoffreshwatercuriosities.com/2012/03/20/diatoms-a-freshwater-curiosity/ Diatoms: A Freshwater Curiosity], The BioFresh Cabinet of Freshwater Curiosities |
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* [http://www.ucl.ac.uk/GeolSci/micropal/diatom.html Diatom life history and ecology] {{Webarchive|url=https://web.archive.org/web/20160202141717/http://www.ucl.ac.uk/GeolSci/micropal/diatom.html |date=2 February 2016 }}, Microfossil Image Recovery and Circulation for Learning and Education (MIRACLE), [[University College London]] |
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* [http://hjs.geol.uib.no/Diatoms/index.html-ssi Diatoms: 'Nature's Marbles'], Eureka site, [[University of Bergen]] |
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* [http://www.rbge.org.uk/science/cryptogamic-plants-and-fungi/phycology/diatoms Diatom page] {{Webarchive|url=https://web.archive.org/web/20091008014752/http://www.rbge.org.uk/science/cryptogamic-plants-and-fungi/phycology/diatoms |date=8 October 2009 }}, [[Royal Botanic Garden Edinburgh]] |
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* [http://www.ucl.ac.uk/GeolSci/micropal/diatom.html Diatom life history and ecology], Microfossil Image Recovery and Circulation for Learning and Education (MIRACLE), [[University College London]] |
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* [http://www.rbge.org.uk/science/cryptogamic-plants-and-fungi/phycology/diatoms Diatom page], [[Royal Botanic Garden Edinburgh]] |
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* [http://www.microscopy-uk.org.uk/mag/artfeb05/cbdiatoms.html Geometry and Pattern in Nature 3: The holes in radiolarian and diatom tests] |
* [http://www.microscopy-uk.org.uk/mag/artfeb05/cbdiatoms.html Geometry and Pattern in Nature 3: The holes in radiolarian and diatom tests] |
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* [https://web.archive.org/web/20080523203035/http://www.mbari.org/staff/conn/botany/phytoplankton/phytoplankton_diatoms.htm Diatom QuickFacts], [[Monterey Bay Aquarium Research Institute]] |
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* [http://www1.tip.nl/%7Et936927/art_deco.html Art Deco Diatoms], Wim van Egmond |
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* [http://diatom.ansp.org/algae_image/ Algae image database] {{Webarchive|url=https://web.archive.org/web/20110814150634/http://diatom.ansp.org/algae_image/ |date=14 August 2011 }} [[Academy of Natural Sciences of Philadelphia]] (ANSP) |
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* [http://www.mbari.org/staff/conn/botany/phytoplankton/phytoplankton_diatoms.htm Diatom QuickFacts], [[Monterey Bay Aquarium Research Institute]] |
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* [http://diatom.ansp.org/ |
* [http://diatom.ansp.org/nawqa/Taxalist.aspx Diatom taxa] {{Webarchive|url=https://web.archive.org/web/20111003144909/http://diatom.ansp.org/nawqa/Taxalist.aspx |date=3 October 2011 }} [[Academy of Natural Sciences of Philadelphia]] (ANSP) |
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* [http://www.microscopy-uk.org.uk/diatomist/rbm_US_Royal.pdf An Introduction to the Microscopical Study of Diatoms] {{Webarchive|url=https://web.archive.org/web/20220805070607/http://www.microscopy-uk.org.uk/diatomist/rbm_US_Royal.pdf |date=5 August 2022 }} by Robert B. McLaughlin |
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* [http://diatom.ansp.org/nawqa/Taxalist.aspx Diatom taxa] [[Academy of Natural Sciences of Philadelphia]] (ANSP) |
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* [http://www.deccanherald.com/content/20100/now-energy-single-celled-algae.html/ Now, energy from single celled algae] ''[[Deccan Herald]]'' |
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* [http://pubs.acs.org/cgi-bin/abstract.cgi/langd5/asap/abs/la702278f.html Computer simulations of pattern formation in diatoms] |
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* [http://www.mrkism.com/diatomea/ aDiatomea, an artificial life experiment with highly detailed 3d generated diatoms] |
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*[http://www.cmog.org/article/glass-nature Glass in Nature, The Corning Museum of Glass] |
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{{plankton}} |
{{plankton}} |
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{{ |
{{heterokont}} |
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{{Taxonbar|from1=Q162678|from2=Q2878349|from3=Q9642991}} |
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{{Use dmy dates|date=August 2011}} |
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{{Authority control}} |
{{Authority control}} |
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[[Category:Algae |
[[Category:Algae]] |
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[[Category:Biological oceanography]] |
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[[Category:Diatoms|*]] |
[[Category:Diatoms|*]] |
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[[Category:Planktology]] |
<!-- [[Category:Biological oceanography]] [[Category:Planktology]] category:Diatoms already listed --> |
Latest revision as of 21:18, 22 December 2024
Diatom Temporal range:
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Light microscopy of a sampling of marine diatoms found living between crystals of annual sea ice in Antarctica, showing a multiplicity of sizes and shapes | |
Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Stramenopiles |
Phylum: | Gyrista |
Subphylum: | Ochrophytina |
Infraphylum: | Diatomista |
Class: | Bacillariophyceae Dangeard, 1933[1] |
Subclasses[2] | |
| |
Synonyms | |
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A diatom (Neo-Latin diatoma)[a] is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year,[11][12] take in over 6.7 billion tonnes of silicon each year from the waters in which they live,[13] and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.[14][15]
Diatoms are unicellular organisms: they occur either as solitary cells or in colonies, which can take the shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 2000 micrometers.[16] In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by asexual multiple fission; the maximum life span of individual cells is about six days.[17] Diatoms have two distinct shapes: a few (centric diatoms) are radially symmetric, while most (pennate diatoms) are broadly bilaterally symmetric.
The unique feature of diatoms is that they are surrounded by a cell wall made of silica (hydrated silicon dioxide), called a frustule.[18] These frustules produce structural coloration, prompting them to be described as "jewels of the sea" and "living opals".
Movement in diatoms primarily occurs passively as a result of both ocean currents and wind-induced water turbulence; however, male gametes of centric diatoms have flagella, permitting active movement to seek female gametes. Similar to plants, diatoms convert light energy to chemical energy by photosynthesis, but their chloroplasts were acquired in different ways.[19]
Unusually for autotrophic organisms, diatoms possess a urea cycle, a feature that they share with animals, although this cycle is used to different metabolic ends in diatoms. The family Rhopalodiaceae also possess a cyanobacterial endosymbiont called a spheroid body. This endosymbiont has lost its photosynthetic properties, but has kept its ability to perform nitrogen fixation, allowing the diatom to fix atmospheric nitrogen.[20] Other diatoms in symbiosis with nitrogen-fixing cyanobacteria are among the genera Hemiaulus, Rhizosolenia and Chaetoceros.[21]
Dinotoms are diatoms that have become endosymbionts inside dinoflagellates. Research on the dinoflagellates Durinskia baltica and Glenodinium foliaceum has shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimal to no gene loss. The main difference between these and free living diatoms is that they have lost their cell wall of silica, making them the only known shell-less diatoms.[22]
The study of diatoms is a branch of phycology. Diatoms are classified as eukaryotes, organisms with a nuclear envelope-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes. They comprise an integral component of the periphyton community.[23] Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist.
Fossil evidence suggests that diatoms originated during or before the early Jurassic period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms is a specimen of extant genus Hemiaulus in Late Jurassic aged amber from Thailand.[24]
Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. Diatomaceous earth (diatomite) is a collection of diatom shells found in the Earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer.
Overview
[edit]Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans.[28] This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into the deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species [29] that are distributed between the two major diatom groups: centrics and pennates.[30][31]
Morphology
[edit]Diatoms are generally 20 to 200 micrometers in size,[32] with a few larger species. Their yellowish-brown chloroplasts, the site of photosynthesis, are typical of heterokonts, having four cell membranes and containing pigments such as the carotenoid fucoxanthin. Individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, including the hairs (mastigonemes) characteristic in other groups.
Diatoms are often referred as "jewels of the sea" or "living opals" due to their optical properties.[33] The biological function of this structural coloration is not clear, but it is speculated that it may be related to communication, camouflage, thermal exchange and/or UV protection.[34]
Diatoms build intricate hard but porous cell walls called frustules composed primarily of silica.[35]: 25–30 This siliceous wall[36] can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species.
The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half, the hypotheca, is slightly smaller than the other half, the epitheca. Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical. Their distinguishing feature is a hard mineral shell or frustule composed of opal (hydrated, polymerized silicic acid).
Diatoms are divided into two groups that are distinguished by the shape of the frustule: the centric diatoms and the pennate diatoms.
Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces.
Centric diatoms are radially symmetric. They are composed of upper and lower valves – epitheca and hypotheca – each consisting of a valve and a girdle band that can easily slide underneath each other and expand to increase cell content over the diatoms progression. The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content. The cytoplasmic layer is home to several organelles, like the chloroplasts and mitochondria. Before the centric diatom begins to expand, its nucleus is at the center of one of the valves and begins to move towards the center of the cytoplasmic layer before division is complete. Centric diatoms have a variety of shapes and sizes, depending on from which axis the shell extends, and if spines are present.
Silicification
[edit]Diatom cells are contained within a unique silica cell wall known as a frustule made up of two valves called thecae, that typically overlap one another.[41] The biogenic silica composing the cell wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two-halves and grows a smaller half within it. As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore, usually through meiosis and sexual reproduction, but exceptions exist. The auxospore expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions.[42]
The exact mechanism of transferring silica absorbed by the diatom to the cell wall is unknown. Much of the sequencing of diatom genes comes from the search for the mechanism of silica uptake and deposition in nano-scale patterns in the frustule. The most success in this area has come from two species, Thalassiosira pseudonana, which has become the model species, as the whole genome was sequenced and methods for genetic control were established, and Cylindrotheca fusiformis, in which the important silica deposition proteins silaffins were first discovered.[44] Silaffins, sets of polycationic peptides, were found in C. fusiformis cell walls and can generate intricate silica structures. These structures demonstrated pores of sizes characteristic to diatom patterns. When T. pseudonana underwent genome analysis it was found that it encoded a urea cycle, including a higher number of polyamines than most genomes, as well as three distinct silica transport genes.[45] In a phylogenetic study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species.[44] This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms. The sequences compared in this study were used to create a diverse background in order to identify residues that differentiate function in the silica deposition process. Additionally, the same study found that a number of the regions were conserved within species, likely the base structure of silica transport.
These silica transport proteins are unique to diatoms, with no homologs found in other species, such as sponges or rice. The divergence of these silica transport genes is also indicative of the structure of the protein evolving from two repeated units composed of five membrane bound segments, which indicates either gene duplication or dimerization.[44] The silica deposition that takes place from the membrane bound vesicle in diatoms has been hypothesized to be a result of the activity of silaffins and long chain polyamines. This Silica Deposition Vesicle (SDV) has been characterized as an acidic compartment fused with Golgi-derived vesicles.[46] These two protein structures have been shown to create sheets of patterned silica in-vivo with irregular pores on the scale of diatom frustules. One hypothesis as to how these proteins work to create complex structure is that residues are conserved within the SDV's, which is unfortunately difficult to identify or observe due to the limited number of diverse sequences available. Though the exact mechanism of the highly uniform deposition of silica is as yet unknown, the Thalassiosira pseudonana genes linked to silaffins are being looked to as targets for genetic control of nanoscale silica deposition.
The ability of diatoms to make silica-based cell walls has been the subject of fascination for centuries. It started with a microscopic observation by an anonymous English country nobleman in 1703, who observed an object that looked like a chain of regular parallelograms and debated whether it was just crystals of salt, or a plant.[47] The viewer decided that it was a plant because the parallelograms didn't separate upon agitation, nor did they vary in appearance when dried or subjected to warm water (in an attempt to dissolve the "salt"). Unknowingly, the viewer's confusion captured the essence of diatoms—mineral utilizing plants. It is not clear when it was determined that diatom cell walls are made of silica, but in 1939 a seminal reference characterized the material as silicic acid in a "subcolloidal" state[48] Identification of the main chemical component of the cell wall spurred investigations into how it was made. These investigations have involved, and been propelled by, diverse approaches including, microscopy, chemistry, biochemistry, material characterisation, molecular biology, 'omics, and transgenic approaches. The results from this work have given a better understanding of cell wall formation processes, establishing fundamental knowledge which can be used to create models that contextualise current findings and clarify how the process works.[49]
The process of building a mineral-based cell wall inside the cell, then exporting it outside, is a massive event that must involve large numbers of genes and their protein products. The act of building and exocytosing this large structural object in a short time period, synched with cell cycle progression, necessitates substantial physical movements within the cell as well as dedication of a significant proportion of the cell's biosynthetic capacities.[49]
The first characterisations of the biochemical processes and components involved in diatom silicification were made in the late 1990s.[50][51][52] These were followed by insights into how higher order assembly of silica structures might occur.[53][54][55] More recent reports describe the identification of novel components involved in higher order processes, the dynamics documented through real-time imaging, and the genetic manipulation of silica structure.[56][57] The approaches established in these recent works provide practical avenues to not only identify the components involved in silica cell wall formation but to elucidate their interactions and spatio-temporal dynamics. This type of holistic understanding will be necessary to achieve a more complete understanding of cell wall synthesis.[49]
Behaviour
[edit]Most centric and araphid pennate diatoms are nonmotile, and their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains.[58] These adaptations increase their surface area to volume ratio and drag, allowing them to stay suspended in the water column longer. Individual cells may regulate buoyancy via an ionic pump.[59]
Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through a seamlike structure called the raphe.[60][61] In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to.
Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; mucilage pads, stalks or tubes; amorphous masses of mucilage; or by threads of chitin (polysaccharide), which are secreted through strutted processes of the cell.
Life cycle
[edit]Reproduction and cell size
[edit]Reproduction among these organisms is asexual by binary fission, during which the diatom divides into two parts, producing two "new" diatoms with identical genes. Each new organism receives one of the two frustules – one larger, the other smaller – possessed by the parent, which is now called the epitheca; and is used to construct a second, smaller frustule, the hypotheca. The diatom that received the larger frustule becomes the same size as its parent, but the diatom that received the smaller frustule remains smaller than its parent. This causes the average cell size of this diatom population to decrease.[16] It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size.[62] Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and auxospore formation must occur.[16]
Cell division
[edit]Vegetative cells of diatoms are diploid (2N) and so meiosis can take place, producing male and female gametes which then fuse to form the zygote. The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve.[35]
A defining characteristic of all diatoms is their restrictive and bipartite silica cell wall that causes them to progressively shrink during asexual cell division. At a critically small cell size and under certain conditions, auxosporulation restitutes cell size and prevents clonal death.[63][64][65][66][67] The entire lifecycles of only a few diatoms have been described and rarely have sexual events been captured in the environment.[31]
Sexual reproduction
[edit]Most eukaryotes are capable of sexual reproduction involving meiosis. Sexual reproduction appears to be an obligatory phase in the life cycle of diatoms, particularly as cell size decreases with successive vegetative divisions.[68] Sexual reproduction involves production of gametes and the fusion of gametes to form a zygote in which maximal cell size is restored.[68] The signaling that triggers the sexual phase is favored when cells accumulate together, so that the distance between them is reduced and the contacts and/or the perception of chemical cues is facilitated.[69]
An exploration of the genomes of five diatoms and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis.[70] Thus a meiotic toolkit appears to be conserved in these six diatom species,[70] indicating a central role of meiosis in diatoms as in other eukaryotes.
Sperm motility
[edit]Diatoms are mostly non-motile; however, sperm found in some species can be flagellated, though motility is usually limited to a gliding motion.[35] In centric diatoms, the small male gametes have one flagellum while the female gametes are large and non-motile (oogamous). Conversely, in pennate diatoms both gametes lack flagella (isogamous).[16] Certain araphid species, that is pennate diatoms without a raphe (seam), have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.[62]
Degradation by microbes
[edit]Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using hydrolytic enzymes to break down the organic algal material.[71][72]
Ecology
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Plankton |
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Distribution
[edit]Diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They are one of the dominant components of phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton.[74] Most live pelagically in open water, although some live as surface films at the water-sediment interface (benthic), or even under damp atmospheric conditions. They are especially important in oceans, where a 2003 study found that they contribute an estimated 45% of the total oceanic primary production of organic material.[75] However, a more recent 2016 study estimates that the number is closer to 20%.[76] Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.[77][35]
Growth
[edit]Planktonic diatoms in freshwater and marine environments typically exhibit a "boom and bust" (or "bloom and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at the spring), their competitive edge and rapid growth rate[74] enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic r-strategists (i.e. those organisms whose ecology is defined by a high growth rate, r).
Impact
[edit]The freshwater diatom Didymosphenia geminata, commonly known as Didymo, causes severe environmental degradation in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an invasive species both in the antipodes and in parts of North America.[78][79] The problem is most frequently recorded from Australia and New Zealand.[80]
When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy resting spores. Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell metabolism). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the thermocline.
Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous upwelling[81]), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents.
In the open ocean, the diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, nitrogen or phosphorus nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus).
Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters[81][82] (see also the biological pump). Significantly, they also play a key role in the regulation of the biogeochemical cycle of silicon in the modern ocean.[75][83]
Reason for success
[edit]Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands.[citation needed] The use of silicon by diatoms is believed by many researchers to be the key to this ecological success. Raven (1983)[84] noted that, relative to organic cell walls, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992)[73] found that diatom dominance of mesocosm communities was directly related to the availability of silicic acid – when concentrations were greater than 2 μmol m−3, they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers[85] have suggested that the biogenic silica in diatom cell walls acts as an effective pH buffering agent, facilitating the conversion of bicarbonate to dissolved CO2 (which is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size.[74]
Sources for collection
[edit]Diatoms can be obtained from multiple sources.[86] Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping barnacles, oyster and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. Cladophora is frequently covered with Cocconeis, an elliptically shaped diatom; Vaucheria is often covered with small forms. Since diatoms form an important part of the food of molluscs, tunicates, and fishes, the alimentary tracts of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated.[86]
Biogeochemistry
[edit]-
The modern oceanic silicon cycle
Fluxes are in Tmol Si y−1 (1 Tmol = 28 million metric tons of silicon)
Silica cycle
[edit]The diagram shows the major fluxes of silicon in the current ocean. Most biogenic silica in the ocean (silica produced by biological activity) comes from diatoms. Diatoms extract dissolved silicic acid from surface waters as they grow, and return it to the water column when they die. Inputs of silicon arrive from above via aeolian dust, from the coasts via rivers, and from below via seafloor sediment recycling, weathering, and hydrothermal activity.[83]
Although diatoms may have existed since the Triassic, the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean's silicon cycle.[87][88][89] Subsequently, the cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges, the former as zooplankton, the latter as sedentary filter-feeders primarily on the continental shelves.[90] Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms.
However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves,[91] suggests that this takeover began in the Cretaceous (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the Cenozoic (66 Ma to present).[92]
-
Ocean carbon cycle and diatom carbon dioxide concentration mechanisms [93]
Carbon cycle
[edit]The diagram depicts some mechanisms by which marine diatoms contribute to the biological carbon pump and influence the ocean carbon cycle. The anthropogenic CO2 emission to the atmosphere (mainly generated by fossil fuel burning and deforestation) is nearly 11 gigatonne carbon (GtC) per year, of which almost 2.5 GtC is taken up by the surface ocean. In surface seawater (pH 8.1–8.4), bicarbonate (HCO−
3) and carbonate ions (CO2−
3) constitute nearly 90 and <10% of dissolved inorganic carbon (DIC) respectively, while dissolved CO2 (CO2 aqueous) contributes <1%. Despite this low level of CO2 in the ocean and its slow diffusion rate in water, diatoms fix 10–20 GtC annually via photosynthesis thanks to their carbon dioxide concentrating mechanisms, allowing them to sustain marine food chains. In addition, 0.1–1% of this organic material produced in the euphotic layer sinks down as particles, thus transferring the surface carbon toward the deep ocean and sequestering atmospheric CO2 for thousands of years or longer. The remaining organic matter is remineralized through respiration. Thus, diatoms are one of the main players in this biological carbon pump, which is arguably the most important biological mechanism in the Earth System allowing CO2 to be removed from the carbon cycle for very long period.[94][93]
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Mitochondrial urea cycle in a generic diatom cell and the potential fates of urea cycle intermediates [95]
Urea cycle
[edit]A feature of diatoms is the urea cycle, which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have a functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the metazoans which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not.[96]
While often overlooked in photosynthetic organisms, the mitochondria also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under ammonium (NH+
4) nutrition compared with nitrate (NO−
3) nutrition. First, in diatoms, and likely some other algae, there is a urea cycle.[97][98][99] The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by amino acid Catabolism; like photorespiration, the urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the cytoplasm, and potentially the plastid [100] and may help to regulate ammonium metabolism.[97][98] Because of this cycle, marine diatoms, in contrast to chlorophytes, also have acquired a mitochondrial urea transporter and, in fact, based on bioinformatics, a complete mitochondrial GS-GOGAT cycle has been hypothesised.[98][95]
Other
[edit]Diatoms are mainly photosynthetic; however a few are obligate heterotrophs and can live in the absence of light provided an appropriate organic carbon source is available.[101][102]
Photosynthetic diatoms that find themselves in an environment absent of oxygen and/or sunlight can switch to anaerobic respiration known as nitrate respiration (DNRA), and stay dormant for up till months and decades.[103][104]
Major pigments of diatoms are chlorophylls a and c, beta-carotene, fucoxanthin, diatoxanthin and diadinoxanthin.[16]
Taxonomy
[edit]Diatoms belong to a large group of protists, many of which contain plastids rich in chlorophylls a and c. The group has been variously referred to as heterokonts, chrysophytes, chromists or stramenopiles. Many are autotrophs such as golden algae and kelp; and heterotrophs such as water moulds, opalinids, and actinophryid heliozoa. The classification of this area of protists is still unsettled. In terms of rank, they have been treated as a division, phylum, kingdom, or something intermediate to those. Consequently, diatoms are ranked anywhere from a class, usually called Diatomophyceae or Bacillariophyceae, to a division (=phylum), usually called Bacillariophyta, with corresponding changes in the ranks of their subgroups.
Genera and species
[edit]An estimated 20,000 extant diatom species are believed to exist, of which around 12,000 have been named to date according to Guiry, 2012[105] (other sources give a wider range of estimates[16][106][107][108]). Around 1,000–1,300 diatom genera have been described, both extant and fossil,[109][110] of which some 250–300 exist only as fossils.[111]
Classes and orders
[edit]For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class Coscinodiscophyceae, but splitting the former pennate diatoms into 2 separate classes, Fragilariophyceae and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new.
Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as AlgaeBase, the World Register of Marine Species and its contributing database DiatomBase, and the system for "all life" represented in Ruggiero et al., 2015, all retain the Round et al. treatment as their basis, albeit with diatoms as a whole treated as a class rather than division/phylum, and Round et al.'s classes reduced to subclasses, for better agreement with the treatment of phylogenetically adjacent groups and their containing taxa. (For references refer the individual sections below).
One proposal, by Linda Medlin and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae-Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 Handbook of the Protists edited by Archibald et al., with some modifications reflecting the apparent non-monophyly of Medlin et al. original "Coscinodiscophyceae". Meanwhile, a group led by E.C. Theriot favours a different hypothesis of phylogeny, which has been termed the structural gradation hypothesis (SGH) and does not recognise the Mediophyceae as a monophyletic group, while another analysis, that of Parks et al., 2018, finds that the radial centric diatoms (Medlin et al.'s Coscinodiscophyceae) are not monophyletic, but supports the monophyly of Mediophyceae minus Attheya, which is an anomalous genus. Discussion of the relative merits of these conflicting schemes continues by the various parties involved.[112][113][114][115]
Adl et al., 2019 treatment
[edit]In 2019, Adl et al.[116] presented the following classification of diatoms, while noting: "This revision reflects numerous advances in the phylogeny of the diatoms over the last decade. Due to our poor taxon sampling outside of the Mediophyceae and pennate diatoms, and the known and anticipated diversity of all diatoms, many clades appear at a high classification level (and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed).
- Clade Diatomista Derelle et al. 2016, emend. Cavalier-Smith 2017 (diatoms plus a subset of other ochrophyte groups)
- Phylum Diatomeae Dumortier 1821 [= Bacillariophyta Haeckel 1878] (diatoms)
- Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019
- Class Leptocylindrophyceae D.G. Mann in Adl et al. 2019 (Leptocylindrus, Tenuicylindrus)
- Class Corethrophyceae D.G. Mann in Adl et al. 2019 (Corethron)
- Subphylum Ellerbeckiophytina D.G. Mann in Adl et al. 2019 (Ellerbeckia)
- Subphylum Probosciophytina D.G. Mann in Adl et al. 2019 (Proboscia)
- Subphylum Melosirophytina D.G. Mann in Adl et al. 2019 (Aulacoseira, Melosira, Hyalodiscus, Stephanopyxis, Paralia, Endictya)
- Subphylum Coscinodiscophytina Medlin & Kaczmarska 2004, emend. (Actinoptychus, Coscinodiscus, Actinocyclus, Asteromphalus, Aulacodiscus, Stellarima)
- Subphylum Rhizosoleniophytina D.G. Mann in Adl et al. 2019 (Guinardia, Rhizosolenia, Pseudosolenia)
- Subphylum Arachnoidiscophytina D.G. Mann in Adl et al. 2019 (Arachnoidiscus)
- Subphylum Bacillariophytina Medlin & Kaczmarska 2004, emend.
- Class Mediophyceae Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004
- Subclass Chaetocerotophycidae Round & R.M. Crawford in Round et al. 1990, emend.
- Subclass Lithodesmiophycidae Round & R.M. Crawford in Round et al. 1990, emend.
- Subclass Thalassiosirophycidae Round & R.M. Crawford in Round et al. 1990
- Subclass Cymatosirophycidae Round & R.M. Crawford in Round et al. 1990
- Subclass Odontellophycidae D.G. Mann in Adl et al. 2019
- Subclass Chrysanthemodiscophycidae D.G. Mann in Adl et al. 2019
- Class Biddulphiophyceae D.G. Mann in Adl et al. 2019
- Subclass Biddulphiophycidae Round and R.M. Crawford in Round et al. 1990, emend.
- Biddulphiophyceae incertae sedis (Attheya)
- Class Bacillariophyceae Haeckel 1878, emend.
- Bacillariophyceae incertae sedis (Striatellaceae)
- Subclass Urneidophycidae Medlin 2016
- Subclass Fragilariophycidae Round in Round, Crawford & Mann 1990, emend.
- Subclass Bacillariophycidae D.G. Mann in Round, Crawford & Mann 1990, emend.
- Class Mediophyceae Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004
- Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019
- Phylum Diatomeae Dumortier 1821 [= Bacillariophyta Haeckel 1878] (diatoms)
See taxonomy of diatoms for more details.
Gallery
[edit]-
Diatom Surirella spiralis
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Diatoms Thalassiosira sp. on a membrane filter, pore size 0.4 μm.
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Diatom Paralia sulcata.
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Diatom Achanthes trinodis
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Stand-alone cell of Bacillaria paxillifer
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Colonial group of Bacillaria paxillifer
External videos | |
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Bacillaria: Distractingly Beautiful Crystal Colonies – Journey to the Microcosmos: |
Three diatom species were sent to the International Space Station, including the huge (6 mm length) diatoms of Antarctica and the exclusive colonial diatom, Bacillaria paradoxa. The cells of Bacillaria moved next to each other in partial but opposite synchrony by a microfluidics method.[117]
Evolution and fossil record
[edit]Origin
[edit]Heterokont chloroplasts appear to derive from those of red algae, rather than directly from prokaryotes as occurred in plants. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record.
Earliest fossils
[edit]The earliest known fossil diatoms date from the early Jurassic (~185 Ma ago),[118] although the molecular clock[118] and sedimentary[119] evidence suggests an earlier origin. It has been suggested that their origin may be related to the end-Permian mass extinction (~250 Ma), after which many marine niches were opened.[120] The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was cryptic.[121] Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early Cretaceous, and with some rocks such as diatomaceous earth, being composed almost entirely of them.
Relation to grasslands
[edit]The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era.[122][123] Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.[124]
Relation to climate
[edit]Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios,[125] could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.[124]
Method of investigation
[edit]The fossil record of diatoms has largely been established through the recovery of their siliceous frustules in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom biostratigraphy, which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land.[126] Where diatom biozones are well established and calibrated to the geomagnetic polarity time scale (e.g., Southern Ocean, North Pacific, eastern equatorial Pacific), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for Cenozoic diatom assemblages is several hundred thousand years.
Diatoms preserved in lake sediments are widely used for paleoenvironmental reconstructions of Quaternary climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity.
Isotope records
[edit]When diatoms die their shells (frustules) can settle on the seafloor and become microfossils. Over time, these microfossils become buried as opal deposits in the marine sediment. Paleoclimatology is the study of past climates. Proxy data is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. Paleoclimate proxies refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements.[127] An example of proxies is the use of diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, and δ30Sidiatom). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west Pacific Ocean, including nutrient supply and the efficiency of the soft-tissue biological pump, from the modern day back to marine isotope stage 5e, which coincides with the last interglacial period. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone.[128]
The initial development of the halocline and stratified water column has been attributed to the onset of major Northern Hemisphere glaciation at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and sea surface temperatures.[129][130][131][132] The decrease of abyssal water upwelling associated with this may have contributed to the establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma.[130] While the halocline appears to have prevailed through the late Pliocene and early Quaternary glacial–interglacial cycles,[133] other studies have shown that the stratification boundary may have broken down in the late Quaternary at glacial terminations and during the early part of interglacials.[134][135][136][137][138][128]
Diversification
[edit]The Cretaceous record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The Cretaceous–Paleogene extinction event, which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.[139]
Turnover
[edit]Although no mass extinctions of marine diatoms have been observed during the Cenozoic, times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the Paleocene–Eocene boundary,[140] and at the Eocene–Oligocene boundary.[141] Further turnover of assemblages took place at various times between the middle Miocene and late Pliocene,[142] in response to progressive cooling of polar regions and the development of more endemic diatom assemblages.
A global trend toward more delicate diatom frustules has been noted from the Oligocene to the Quaternary.[126] This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major ice sheet expansion on Antarctica and progressive cooling through the Neogene and Quaternary towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic upwelling.
Genetics
[edit]Expressed sequence tagging
[edit]In 2002, the first insights into the properties of the Phaeodactylum tricornutum gene repertoire were described using 1,000 expressed sequence tags (ESTs).[143] Subsequently, the number of ESTs was extended to 12,000 and the diatom EST database was constructed for functional analyses.[144] These sequences have been used to make a comparative analysis between P. tricornutum and the putative complete proteomes from the green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae, and the diatom Thalassiosira pseudonana.[145] The diatom EST database now consists of over 200,000 ESTs from P. tricornutum (16 libraries) and T. pseudonana (7 libraries) cells grown in a range of different conditions, many of which correspond to different abiotic stresses.[146]
Genome sequencing
[edit]In 2004, the entire genome of the centric diatom, Thalassiosira pseudonana (32.4 Mb) was sequenced,[147] followed in 2008 with the sequencing of the pennate diatom, Phaeodactylum tricornutum (27.4 Mb).[148] Comparisons of the two reveal that the P. tricornutum genome includes fewer genes (10,402 opposed to 11,776) than T. pseudonana; no major synteny (gene order) could be detected between the two genomes. T. pseudonana genes show an average of ~1.52 introns per gene as opposed to 0.79 in P. tricornutum, suggesting recent widespread intron gain in the centric diatom.[148][149] Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the Bacillariophyceae compared to other eukaryotic groups.[148] Comparative genomics also established that a specific class of transposable elements, the Diatom Copia-like retrotransposons (or CoDis), has been significantly amplified in the P. tricornutum genome with respect to T. pseudonana, constituting 5.8 and 1% of the respective genomes.[150]
Endosymbiotic gene transfer
[edit]Diatom genomics brought much information about the extent and dynamics of the endosymbiotic gene transfer (EGT) process. Comparison of the T. pseudonana proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage. EGT towards diatom genomes can be illustrated by the fact that the T. pseudonana genome encodes six proteins which are most closely related to genes encoded by the Guillardia theta (cryptomonad) nucleomorph genome. Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus.[147] More recent phylogenomic analyses of diatom proteomes provided evidence for a prasinophyte-like endosymbiont in the common ancestor of chromalveolates as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other stramenopiles. Therefore, it was proposed that chromalveolates are the product of serial secondary endosymbiosis first with a green algae, followed by a second one with a red algae that conserved the genomic footprints of the previous but displaced the green plastid.[151] However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under-sequenced lineages such as red algae.
Horizontal gene transfer
[edit]In addition to EGT, horizontal gene transfer (HGT) can occur independently of an endosymbiotic event. The publication of the P. tricornutum genome reported that at least 587 P. tricornutum genes appear to be most closely related to bacterial genes, accounting for more than 5% of the P. tricornutum proteome. About half of these are also found in the T. pseudonana genome, attesting their ancient incorporation in the diatom lineage.[148]
Genetic engineering
[edit]To understand the biological mechanisms which underlie the great importance of diatoms in geochemical cycles, scientists have used the Phaeodactylum tricornutum and Thalassiosira spp. species as model organisms since the 90's.[152] Few molecular biology tools are currently available to generate mutants or transgenic lines : plasmids containing transgenes are inserted into the cells using the biolistic method[153] or transkingdom bacterial conjugation[154] (with 10−6 and 10−4 yield respectively[153][154]), and other classical transfection methods such as electroporation or use of PEG have been reported to provide results with lower efficiencies.[154]
Transfected plasmids can be either randomly integrated into the diatom's chromosomes or maintained as stable circular episomes (thanks to the CEN6-ARSH4-HIS3 yeast centromeric sequence[154]). The phleomycin/zeocin resistance gene Sh Ble is commonly used as a selection marker,[152][155] and various transgenes have been successfully introduced and expressed in diatoms with stable transmissions through generations,[154][155] or with the possibility to remove it.[155]
Furthermore, these systems now allow the use of the CRISPR-Cas genome edition tool, leading to a fast production of functional knock-out mutants[155][156] and a more accurate comprehension of the diatoms' cellular processes.
Human uses
[edit]-
Diatomaceous earth consisting of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms suspended in water.
(click 3 times to fully enlarge)
Paleontology
[edit]Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata (see siliceous ooze).
Industrial
[edit]Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology.[157]
Diatomite is considered to be a natural nano material and has many uses and applications such as: production of various ceramic products, construction ceramics, refractory ceramics, special oxide ceramics, for production of humidity control materials, used as filtration material, material in the cement production industry, initial material for production of prolonged-release drug carriers, absorption material in an industrial scale, production of porous ceramics, glass industry, used as catalyst support, as a filler in plastics and paints, purification of industrial waters, pesticide holder, as well as for improving the physical and chemical characteristics of certain soils, and other uses.[158][159][160]
Diatoms are also used to help determine the origin of materials containing them, including seawater.
Nanotechnology
[edit]The deposition of silica by diatoms may also prove to be of utility to nanotechnology.[161] Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems; semiconductor nanolithography; and even vehicles for drug delivery. With an appropriate artificial selection procedure, diatoms that produce valves of particular shapes and sizes might be evolved for cultivation in chemostat cultures to mass-produce nanoscale components.[162] It has also been proposed that diatoms could be used as a component of solar cells by substituting photosensitive titanium dioxide for the silicon dioxide that diatoms normally use to create their cell walls.[163] Diatom biofuel producing solar panels have also been proposed.[164]
-
CNN = cloud condensation nuclei, DMS = dimethylsulphide, DMSP = dimethylsulfoniopropionate, VOCs = volatile organic compounds
dashed arrow: negative effect, solid arrow: positive effects
Forensic
[edit]The main goal of diatom analysis in forensics is to differentiate a death by submersion from a post-mortem immersion of a body in water. Laboratory tests may reveal the presence of diatoms in the body. Since the silica-based skeletons of diatoms do not readily decay, they can sometimes be detected even in heavily decomposed bodies. As they do not occur naturally in the body, if laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good evidence of drowning as the cause of death. The blend of diatom species found in a corpse may be the same or different from the surrounding water, indicating whether the victim drowned in the same site in which the body was found.[165]
History of discovery
[edit]The first illustrations of diatoms are found in an article from 1703 in Transactions of the Royal Society showing unmistakable drawings of Tabellaria.[166] Although the publication was authored by an unnamed English gentleman, there is recent evidence that he was Charles King of Staffordshire.[166][167] It is only 80 years later that we find the first formally identified diatom, the colonial Bacillaria paxillifera, discovered and described in 1783 by Danish naturalist Otto Friedrich Müller.[166] Like many others after him, he wrongly thought that it was an animal due to its ability to move. Even Charles Darwin saw diatom remains in dust whilst in the Cape Verde Islands, although he was not sure what they were. It was only later that they were identified for him as siliceous polygastrics. The infusoria that Darwin later noted in the face paint of Fueguinos, native inhabitants of Tierra del Fuego in the southern end of South America, were later identified in the same way. During his lifetime, the siliceous polygastrics were clarified as belonging to the Diatomaceae, and Darwin struggled to understand the reasons underpinning their beauty. He exchanged opinions with the noted cryptogamist G. H. K. Thwaites on the topic. In the fourth edition of On the Origin of Species he stated that "Few objects are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the high powers of the microscope"? and reasoned that their exquisite morphologies must have functional underpinnings rather than having been created purely for humans to admire.[168]
See also
[edit]- Highly branched isoprenoid, long-chain alkenes produced by a small number of marine diatoms
Notes
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External links
[edit]- Diatom EST database, École Normale Supérieure
- Plankton*Net, taxonomic database including images of diatom species
- Life History and Ecology of Diatoms, University of California Museum of Paleontology
- Diatoms: 'Nature's Marbles', Eureka site, University of Bergen
- Diatom life history and ecology Archived 2 February 2016 at the Wayback Machine, Microfossil Image Recovery and Circulation for Learning and Education (MIRACLE), University College London
- Diatom page Archived 8 October 2009 at the Wayback Machine, Royal Botanic Garden Edinburgh
- Geometry and Pattern in Nature 3: The holes in radiolarian and diatom tests
- Diatom QuickFacts, Monterey Bay Aquarium Research Institute
- Algae image database Archived 14 August 2011 at the Wayback Machine Academy of Natural Sciences of Philadelphia (ANSP)
- Diatom taxa Archived 3 October 2011 at the Wayback Machine Academy of Natural Sciences of Philadelphia (ANSP)
- An Introduction to the Microscopical Study of Diatoms Archived 5 August 2022 at the Wayback Machine by Robert B. McLaughlin