Editing Methanogen (section)

==Ecology==
In [[anaerobic environment]]s, methanogens play a vital ecological role, removing excess hydrogen and fermentation products that have been produced by other forms of [[anaerobic respiration]].<ref>{{Cite journal |last1=Thauer |first1=Rudolf K. |last2=Kaster |first2=Anne-Kristin |last3=Seedorf |first3=Henning |last4=Buckel |first4=Wolfgang |last5=Hedderich |first5=Reiner |date=August 2008 |title=Methanogenic archaea: ecologically relevant differences in energy conservation |url=https://www.nature.com/articles/nrmicro1931 |journal=Nature Reviews Microbiology |language=en |volume=6 |issue=8 |pages=579–591 |doi=10.1038/nrmicro1931 |pmid=18587410 |issn=1740-1526|url-access=subscription }}</ref> Methanogens typically thrive in environments in which all [[electron acceptor]]s other than CO<sub>2</sub> (such as [[oxygen]], [[nitrate]], [[ferric iron]] (Fe(III)), and [[sulfate]]) have been depleted. Such environments include wetlands and rice paddy soil, the digestive tracts of various animals (ruminants, arthropods, humans),<ref>{{Cite journal |last1=Chibani |first1=Cynthia Maria |last2=Mahnert |first2=Alexander |last3=Borrel |first3=Guillaume |last4=Almeida |first4=Alexandre |last5=Werner |first5=Almut |last6=Brugère |first6=Jean-François |last7=Gribaldo |first7=Simonetta |last8=Finn |first8=Robert D. |last9=Schmitz |first9=Ruth A. |last10=Moissl-Eichinger |first10=Christine |date=2021-12-30 |title=A catalogue of 1,167 genomes from the human gut archaeome |journal=Nature Microbiology |language=en |volume=7 |issue=1 |pages=48–61 |doi=10.1038/s41564-021-01020-9 |issn=2058-5276 |pmc=8727293 |pmid=34969981}}</ref><ref>{{Cite journal |last1=Protasov |first1=Evgenii |last2=Nonoh |first2=James O. |last3=Kästle Silva |first3=Joana M. |last4=Mies |first4=Undine S. |last5=Hervé |first5=Vincent |last6=Dietrich |first6=Carsten |last7=Lang |first7=Kristina |last8=Mikulski |first8=Lena |last9=Platt |first9=Katja |last10=Poehlein |first10=Anja |last11=Köhler-Ramm |first11=Tim |last12=Miambi |first12=Edouard |last13=Boga |first13=Hamadi I. |last14=Feldewert |first14=Christopher |last15=Ngugi |first15=David K. |date=2023-11-15 |title=Diversity and taxonomic revision of methanogens and other archaea in the intestinal tract of terrestrial arthropods |journal=Frontiers in Microbiology |volume=14 |doi=10.3389/fmicb.2023.1281628 |doi-access=free |issn=1664-302X |pmc=10684969 |pmid=38033561}}</ref><ref>{{Cite journal |last1=Thomas |first1=Courtney M. |last2=Desmond-Le Quéméner |first2=Elie |last3=Gribaldo |first3=Simonetta |last4=Borrel |first4=Guillaume |date=2022-06-10 |title=Factors shaping the abundance and diversity of the gut archaeome across the animal kingdom |url=http://dx.doi.org/10.1038/s41467-022-31038-4 |journal=Nature Communications |volume=13 |issue=1 |page=3358 |doi=10.1038/s41467-022-31038-4 |pmid=35688919 |bibcode=2022NatCo..13.3358T |issn=2041-1723|pmc=9187648 }}</ref> wastewater treatment plants and landfills, deep-water oceanic sediments, and hydrothermal vents.<ref>{{Cite journal |last1=Lyu |first1=Zhe |last2=Shao |first2=Nana |last3=Akinyemi |first3=Taiwo |last4=Whitman |first4=William B. |date=July 2018 |title=Methanogenesis |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982218306237 |journal=Current Biology |language=en |volume=28 |issue=13 |pages=R727–R732 |doi=10.1016/j.cub.2018.05.021|pmid=29990451 |bibcode=2018CBio...28.R727L }}</ref> Most of these environments are not categorized as extreme, and thus the methanogens inhabiting them are also not considered extremophiles. However, many well-studied methanogens are thermophiles such as ''[[Methanopyrus kandleri]]'', ''[[Methanothermobacter marburgensis]]'', ''[[Methanocaldococcus jannaschii]]''. On the other hand, gut methanogens such as ''[[Methanobrevibacter smithii]]'' common in humans or ''Methanobrevibacter ruminantium'' omnipresent in ruminants are [[mesophile]]s.{{cn|date=March 2025}}

=== Methanogens in extreme environments ===
In deep [[basalt]]ic rocks near the [[mid-ocean ridge]]s, methanogens can obtain their [[hydrogen]] from the [[serpentinization]] reaction of [[olivine]] as observed in the [[Lost City (hydrothermal field)|hydrothermal field of Lost City]]. The thermal breakdown of water and water [[radiolysis]] are other possible sources of hydrogen. Methanogens are key agents of remineralization of [[organic carbon]] in [[continental margin]] sediments and other aquatic sediments with high rates of sedimentation and high sediment organic matter. Under the correct conditions of pressure and temperature, biogenic methane can accumulate in massive deposits of [[methane clathrate]]s<ref name="Kvenvolden 1995">{{cite journal| last=Kvenvolden| first= K.| date=1995| title= A review of the geochemistry of methane in natural gas hydrate| journal= Organic Geochemistry| volume=23| issue=11–12| pages=997–1008| doi= 10.1016/0146-6380(96)00002-2| bibcode= 1995OrGeo..23..997K}}</ref> that account for a significant fraction of organic carbon in continental margin sediments and represent a key reservoir of a potent greenhouse gas.<ref name="Milkov 2004">{{cite journal|last=Milkov| first=Alexei V| date=2004| title= Global estimates of hydrate-bound gas in marine sediments: how much is really out there?| journal= Earth-Science Reviews| volume=66| issue=3–4| pages=183–197| doi=10.1016/j.earscirev.2003.11.002| bibcode=2004ESRv...66..183M}}</ref>

Methanogens have been found in several extreme environments on Earth – buried under kilometres of ice in [[Greenland]] and living in hot, dry desert soil. They are known to be the most common archaea in deep subterranean habitats. Live microbes making methane were found in a glacial ice core sample retrieved from about three kilometres under Greenland by researchers from the [[University of California, Berkeley]]. They also found a constant metabolism able to repair macromolecular damage, at temperatures of 145 to –40&nbsp;°C.<ref name=":3">{{Cite journal|doi=10.1073/pnas.0507601102|title=Microbial origin of excess methane in glacial ice and implications for life on Mars|journal=Proceedings of the National Academy of Sciences|volume=102|issue=51|pages=18292–6|year=2005|last1=Tung|first1=H. C.|last2=Bramall|first2=N. E.|last3=Price|first3=P. B.|pmid=16339015|pmc=1308353|bibcode=2005PNAS..10218292T|doi-access=free}}</ref>

Another study<ref name=":4">Icarus (vol. 178, p. 277)cs:Methanogen</ref> has also discovered methanogens in a harsh environment on Earth. Researchers studied dozens of soil and vapour samples from five different desert environments in [[Utah]], [[Idaho]] and [[California]] in the [[United States]], and in [[Canada]] and [[Chile]]. Of these, five soil samples and three vapour samples from the vicinity of the [[Mars Desert Research Station]] in Utah were found to have signs of viable methanogens.<ref name=":5">{{Cite journal |last1=Michał |first1=Burdukiewicz |last2=Gagat |first2=Przemysław |last3=Jabłoński |first3=Sławomir |last4=Chilimoniuk |first4=Jarosław |last5=Gaworski |first5=Michał |last6=Mackiewicz |first6=Paweł |last7=Marcin |first7=Łukaszewicz |date=June 2018 |title=PhyMet 2 : a database and toolkit for phylogenetic and metabolic analyses of methanogens |journal=Environmental Microbiology Reports |language=en |volume=10 |issue=3 |pages=378–382 |doi=10.1111/1758-2229.12648 |issn=1758-2229|doi-access=free |pmid=29624889 |bibcode=2018EnvMR..10..378M }}</ref>

Some scientists have proposed that the presence of methane in the [[Mars|Martian]] atmosphere may be indicative of native methanogens on that planet.<ref>{{cite web|url=http://www.space.com/scienceastronomy/051220_science_tuesday.html|title=Crater Critters: Where Mars Microbes Might Lurk|work=Space.com|date=20 December 2005 |access-date=16 December 2014}}</ref> In June 2019, NASA's [[Curiosity (rover)|Curiosity]] rover detected methane, commonly generated by underground microbes such as methanogens, which signals possibility of [[life on Mars]].<ref>{{cite news|url=https://www.nytimes.com/2019/06/22/science/nasa-mars-rover-life.html|title=NASA Rover on Mars Detects Puff of Gas That Hints at Possibility of Life|work=The New York Times|date=22 June 2019}}</ref>

Closely related to the methanogens are the anaerobic methane oxidizers, which utilize methane as a substrate in conjunction with the reduction of sulfate and nitrate.<ref>{{cite journal | doi=10.1038/440878a | author=Thauer, R. K. |author2=Shima, S. |name-list-style=amp | title=Biogeochemistry: Methane and microbes | journal = Nature | date = 2006 | volume = 440 | issue = 7086| pages=878–879 | pmid=16612369 |bibcode = 2006Natur.440..878T | s2cid=4373591 }}</ref> Most methanogens are [[autotrophic]] producers, but those that [[oxidize]] CH<sub>3</sub>COO<sup>−</sup> are classed as [[chemotroph]] instead.{{cn|date=March 2025}}

=== Methanogens in the digestive tract of animals ===
The digestive tract of animals is characterized by a nutrient-rich and predominantly anaerobic environment, making it an ideal habitat for many microbes, including methanogens. Despite this, methanogens and archaea, in general, were largely overlooked as part of the gut microbiota until recently. However, they play a crucial role in maintaining gut balance by utilizing end products of bacterial fermentation, such as H<sub>2</sub>, acetate, methanol, and methylamines.{{cn|date=March 2025}}

[[Methanobrevibacter smithii]] is the predominant methanogenic archaeon in the [[microbiota]] of the [[gastrointestinal tract|human gut]].<ref>{{cite Q|Q54521537}}</ref> Recent extensive surveys of archaea presence in the animal gut, based on 16S rRNA analysis, have provided a comprehensive view of archaea diversity and abundance.<ref>{{Cite journal |last1=Youngblut |first1=Nicholas D. |last2=Reischer |first2=Georg H. |last3=Dauser |first3=Silke |last4=Maisch |first4=Sophie |last5=Walzer |first5=Chris |last6=Stalder |first6=Gabrielle |last7=Farnleitner |first7=Andreas H. |last8=Ley |first8=Ruth E. |date=2021-10-26 |title=Vertebrate host phylogeny influences gut archaeal diversity |journal=Nature Microbiology |language=en |volume=6 |issue=11 |pages=1443–1454 |doi=10.1038/s41564-021-00980-2 |issn=2058-5276 |pmc=8556154 |pmid=34702978}}</ref><ref>{{Cite journal |last1=Thomas |first1=Courtney M. |last2=Desmond-Le Quéméner |first2=Elie |last3=Gribaldo |first3=Simonetta |last4=Borrel |first4=Guillaume |date=2022-06-10 |title=Factors shaping the abundance and diversity of the gut archaeome across the animal kingdom |journal=Nature Communications |language=en |volume=13 |issue=1 |page=3358 |doi=10.1038/s41467-022-31038-4 |issn=2041-1723 |pmc=9187648 |pmid=35688919|bibcode=2022NatCo..13.3358T }}</ref><ref>{{Cite journal |last1=Protasov |first1=Evgenii |last2=Nonoh |first2=James O. |last3=Kästle Silva |first3=Joana M. |last4=Mies |first4=Undine S. |last5=Hervé |first5=Vincent |last6=Dietrich |first6=Carsten |last7=Lang |first7=Kristina |last8=Mikulski |first8=Lena |last9=Platt |first9=Katja |last10=Poehlein |first10=Anja |last11=Köhler-Ramm |first11=Tim |last12=Miambi |first12=Edouard |last13=Boga |first13=Hamadi I. |last14=Feldewert |first14=Christopher |last15=Ngugi |first15=David K. |date=2023-11-15 |title=Diversity and taxonomic revision of methanogens and other archaea in the intestinal tract of terrestrial arthropods |journal=Frontiers in Microbiology |volume=14 |doi=10.3389/fmicb.2023.1281628 |doi-access=free |issn=1664-302X |pmc=10684969 |pmid=38033561}}</ref> These studies revealed that only a few archaeal lineages are present, with the majority being methanogens, while non-methanogenic archaea are rare and not abundant. Taxonomic classification of archaeal diversity identified that representatives of only three phyla are present in the digestive tracts of animals: Methanobacteriota (order Methanobacteriales), Thermoplasmatota (order Methanomassiliicoccales), and Halobacteriota (orders Methanomicrobiales and Methanosarcinales). However, not all families and genera within these orders were detected in animal guts, but only a few genera, suggesting their specific adaptations to the gut environment.{{cn|date=March 2025}}