Editing Nitrogen fixation (section)

===Microorganisms===
{{Main|Diazotroph}}
Diazotrophs are widespread within domain [[Bacteria]] including [[cyanobacteria]] (e.g. the highly significant ''[[Trichodesmium]]'' and ''[[Cyanothece]]''), [[green sulfur bacteria]], [[purple sulfur bacteria]], [[Azotobacteraceae]], [[rhizobia]] and ''[[Frankia]].''<ref>{{Cite web|url=https://scitechdaily.com/nitrogen-inputs-in-the-ancient-ocean-underappreciated-bacteria-step-into-the-spotlight/|title=Nitrogen Inputs in the Ancient Ocean: Underappreciated Bacteria Step Into the Spotlight|first=Max Planck|last=Institute|date=6 August 2021}}</ref><ref name="Mus-2016">{{cite journal | vauthors = Mus F, Crook MB, Garcia K, Garcia Costas A, Geddes BA, Kouri ED, Paramasivan P, Ryu MH, Oldroyd GE, Poole PS, Udvardi MK, Voigt CA, Ané JM, Peters JW | title = Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes | journal = Applied and Environmental Microbiology | volume = 82 | issue = 13 | pages = 3698–3710 | date = July 2016 | pmid = 27084023 | pmc = 4907175 | doi = 10.1128/AEM.01055-16 | bibcode = 2016ApEnM..82.3698M | veditors = Kelly RM }}</ref> Several obligately anaerobic bacteria fix nitrogen including many (but not all) ''[[Clostridium]]'' spp. Some [[archaea]] such as ''[[Methanosarcina acetivorans]]'' also fix nitrogen,<ref>{{cite journal | vauthors = Dhamad AE, Lessner DJ | title = A CRISPRi-dCas9 System for Archaea and Its Use To Examine Gene Function during Nitrogen Fixation by Methanosarcina acetivorans | journal = Applied and Environmental Microbiology | volume = 86 | issue = 21 | pages = e01402–20 | date = October 2020 | pmid = 32826220 | pmc = 7580536 | doi = 10.1128/AEM.01402-20 | bibcode = 2020ApEnM..86E1402D | veditors = Atomi H }}</ref> and several other [[methanogen]]ic [[taxa]], are significant contributors to nitrogen fixation in oxygen-deficient soils.<ref>{{cite journal | vauthors = Bae HS, Morrison E, Chanton JP, Ogram A | title = Methanogens Are Major Contributors to Nitrogen Fixation in Soils of the Florida Everglades | journal = Applied and Environmental Microbiology | volume = 84 | issue = 7 | pages = e02222–17 | date = April 2018 | pmid = 29374038 | pmc = 5861825 | doi = 10.1128/AEM.02222-17 | bibcode = 2018ApEnM..84E2222B }}</ref>

[[Cyanobacteria]], commonly known as blue-green algae, inhabit nearly all illuminated environments on Earth and play key roles in the carbon and [[nitrogen cycle]] of the [[biosphere]]. In general, cyanobacteria can use various inorganic and organic sources of combined nitrogen, such as [[nitrate]], [[nitrite]], [[ammonium]], [[urea]], or some [[amino acid]]s. Several cyanobacteria strains are also capable of diazotrophic growth, an ability that may have been present in their last common ancestor in the [[Archean]] eon.<ref>{{cite journal | vauthors = Latysheva N, Junker VL, Palmer WJ, Codd GA, Barker D | title = The evolution of nitrogen fixation in cyanobacteria | journal = Bioinformatics | volume = 28 | issue = 5 | pages = 603–606 | date = March 2012 | pmid = 22238262 | doi = 10.1093/bioinformatics/bts008 | doi-access = free }}</ref> Nitrogen fixation not only naturally occurs in soils but also aquatic systems, including both freshwater and marine.<ref name="Pierella Karlusich-2021">{{cite journal | vauthors = Pierella Karlusich JJ, Pelletier E, Lombard F, Carsique M, Dvorak E, Colin S, Picheral M, Cornejo-Castillo FM, Acinas SG, Pepperkok R, Karsenti E, de Vargas C, Wincker P, Bowler C, Foster RA | title = Global distribution patterns of marine nitrogen-fixers by imaging and molecular methods | journal = Nature Communications | volume = 12 | issue = 1 | pages = 4160 | date = July 2021 | pmid = 34230473 | pmc = 8260585 | doi = 10.1038/s41467-021-24299-y | bibcode = 2021NatCo..12.4160P }}</ref><ref>{{Cite journal| vauthors = Ash C |date=2021-08-13| veditors = Ash C, Smith J |title=Some light on diazotrophs |journal=Science|language=en|volume=373|issue=6556|pages=755.7–756|doi=10.1126/science.373.6556.755-g|bibcode=2021Sci...373..755A|s2cid=238709371|issn=0036-8075}}</ref> Indeed, the amount of nitrogen fixed in the ocean is at least as much as that on land.<ref>{{cite journal | vauthors = Kuypers MM, Marchant HK, Kartal B | title = The microbial nitrogen-cycling network | journal = Nature Reviews. Microbiology | volume = 16 | issue = 5 | pages = 263–276 | date = May 2018 | pmid = 29398704 | doi = 10.1038/nrmicro.2018.9 | hdl-access = free | s2cid = 3948918 | hdl = 21.11116/0000-0003-B828-1 }}</ref> The colonial marine cyanobacterium ''[[Trichodesmium]]'' is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally.<ref>{{cite journal | vauthors = Bergman B, Sandh G, Lin S, Larsson J, Carpenter EJ | title = Trichodesmium--a widespread marine cyanobacterium with unusual nitrogen fixation properties | journal = FEMS Microbiology Reviews | volume = 37 | issue = 3 | pages = 286–302 | date = May 2013 | pmid = 22928644 | pmc = 3655545 | doi = 10.1111/j.1574-6976.2012.00352.x }}</ref> Marine surface lichens and non-photosynthetic bacteria belonging in Proteobacteria and Planctomycetes fixate significant atmospheric nitrogen.<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2018/06/180611133453.htm|title=Large-scale study indicates novel, abundant nitrogen-fixing microbes in surface ocean|website=ScienceDaily|access-date=8 June 2019|archive-url=https://web.archive.org/web/20190608024940/https://www.sciencedaily.com/releases/2018/06/180611133453.htm|archive-date=8 June 2019|url-status=live}}</ref> Species of nitrogen fixing cyanobacteria in fresh waters include: ''[[Aphanizomenon]]'' and [[Dolichospermum flosaquae|''Dolichospermum'']] (previously Anabaena).<ref>{{Cite journal| vauthors = Rolff C, Almesjö L, Elmgren R |date=2007-03-05|title=Nitrogen fixation and abundance of the diazotrophic cyanobacterium Aphanizomenon sp. in the Baltic Proper|url=http://www.int-res.com/abstracts/meps/v332/p107-118/|journal=Marine Ecology Progress Series|language=en|volume=332|pages=107–118|doi=10.3354/meps332107 |bibcode=2007MEPS..332..107R|doi-access=free}}</ref> Such species have specialized cells called [[Heterocyst|heterocytes]], in which nitrogen fixation occurs via the nitrogenase enzyme.<ref>{{Cite journal| vauthors = Carmichael WW |date=12 Oct 2001|title=Health Effects of Toxin-Producing Cyanobacteria: "The CyanoHABs" |journal=Human and Ecological Risk Assessment|language=en|volume=7|issue=5|pages=1393–1407|doi=10.1080/20018091095087|bibcode=2001HERA....7.1393C |s2cid=83939897|issn=1080-7039}}</ref><ref>{{cite journal | vauthors = Bothe H, Schmitz O, Yates MG, Newton WE | title = Nitrogen fixation and hydrogen metabolism in cyanobacteria | journal = Microbiology and Molecular Biology Reviews | volume = 74 | issue = 4 | pages = 529–551 | date = December 2010 | pmid = 21119016 | pmc = 3008169 | doi = 10.1128/MMBR.00033-10 }}</ref>