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==Os metanóxenos en ambientes extremos==
Os metanóxenos desempeñan un papel ecolóxico vital nos ambientes anaeróbicos ao eliminaren o exceso de hidróxeno e produtos de fermentación que foron producidos por outras formas de vida. Os metanóxenos prosperan tipicamente en ambientes nos cales non hai outros [[aceptor de electróns|aceptores de electróns]] distintos do CO<sub>2</sub> (como o [[osíxeno]], [[nitrato]], [[ferro]] trivalente, e [[sulfato]]). Nas rochas [[basalto|basálticas]] profundas de áreas próximas ás [[dorsal oceánica|dorsais oceánicas]], poden obter o seu hidróxeno das reaccións de [[serpentinización]] da [[olivina]], como se observou no [[campo hidrotermal da "Cidade perdida"]] (no Atlántico).
Methanogens play the vital ecological role in [[Hypoxia (environmental)|anaerobic environments]] of removing excess hydrogen and fermentation products that have been produced by other forms of [[anaerobic respiration]]. Methanogens typically thrive in environments in which all [[electron acceptor]]s other than CO<sub>2</sub> (such as [[oxygen]], [[nitrate]], trivalent [[iron]], and [[sulfate]]) have been depleted. In deep [[basalt]]ic rocks near the [[mid ocean ridge]]s, they can obtain their [[hydrogen]] from the [[Serpentinite#Serpentinite_reactions|serpentinisation]] reaction of [[olivine]] as observed in the [[Lost City (hydrothermal field)|hydrothermal field of Lost City]].
A rotura termal de moléculas de auga e a [[radiólise]] da auga son outras posibles fontes de hidróxeno.
The thermal breakdown of water and water [[radiolysis]] are other possible sources of hydrogen.
MethanogensAs arearqueas keymetanóxenas agentsson ofaxentes remineralizationfundamentais ofna remineralización do [[organiccarbono carbonorgánico]] innos sedimentos das [[marxe continental|marxes margincontinentais]] sedimentse andoutros othersedimentos aquaticacuáticos sedimentscon withmoita highmateria rates of sedimentation and high sediment organic matterorgánica. Nas Undercondicións theaxeitadas correctde conditionspresión ofe pressuretemperatura, ando temperature,metano biogenicbioxénico methanepode canacumularse accumulatede indepósitos massivemasivos deposits ofde [[methanemetano clathratesclatrato]]s,<ref name="Kvenvolden 1995">{{cite journal| last=Kvenvolden| first= K.| year=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}}</ref> whicho accountque forsupón aunha significantsignificativa fractionfracción ofde organiccarbón carbonorgánico innos continentalsedimentos margindas sedimentsmarxes andcontinentais represente arepresenta keyunha reservoirreserva ofimportante adun potentpotente greenhousegas gasinvernadoiro. <ref name="Milkov 2004">{{cite journal|last=Milkov| first=Alexei V| year=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>
Atopáronse metanóxenos en varios ambientes extremos do planeta: enterrados a varios km de profundidade nos xeos de [[Groenlandia]] <ref>Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0507601102)</ref>, ou vivindo no chan quente e seco do deserto. Poden reproducirse a temperaturas de 15 a 100 graos Celsius. Sábese que son as arqueas máis comúns nos hábitats subterráneos profundos.
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 can reproduce at temperatures of 15 to 100 degrees Celsius. They are known to be the most common archaebacteria in deep subteranean habitats. Live microbes making methane were found in a glacial ice core sample retrieved from three kilometres under Greenland by researchers from the [[University of California, Berkeley]].<ref>Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0507601102)</ref>
AnotherOutro estudo study<ref>Icarus (vol. 178, p. 277)cs:Methanogen</ref> hasdescubriu alsometanóxenos discoverednos methanogensambientes inmáis ainhóspitos harshda environmentTerra. onOs Earth.investigadores Researchersestudaron studiedducias dozensde ofmostras soilde andsolo vapoure samplesvapor fromde fivecinco differentdesertos desertdistintos environments inde [[Utah]], [[Idaho]] ande [[California]] in thenos [[United StatesEEUU]], ande inde [[CanadaCanadá]] ande [[Chile]]. Of theseDeles, fivecinco soilmostras samplesde andsolo threee vapourtres samplesmostras fromde thevapor vicinitytomados of the [[Mars Desert Research Station]] inen Utah werepresentaron foundsignos tode haveconter signsmetanóxenos ofviables. viable methanogens.<ref>[http://www.newscientistspace.com/article/dn8428-extreme-bugs-back-idea-of-life-on-mars.html Extreme bugs back idea of life on Mars]</ref>
SomeAlgúns scientistscientíficos havepropuxeron proposedque thata thepresenza presencede ofmetano methanena in theatmosfera [[MarsMarte|Martianmarciana]] atmospherepode mayser beun indicativeindicativo ofda nativepresenza methanogensde onmetanóxenos thatnativos planetdese planeta. <ref>[http://www.space.com/scienceastronomy/051220_science_tuesday.html Crater Critters: Where Mars Microbes Might Lurk]</ref>
CloselyMoi relatedrelacionados tocos themetanóxenos methanogensestán areos theoxidadores anaerobicanaeróbicos methanedo oxidizersmetano, whichos utilizecales methaneutilizan aso ametano substratecomo inun conjunctionsubstrato withxunto thecoa reductionredución ofdo sulfatesulfato ande nitratenitrato. <ref>{{cite journal | doi=10.1038/440878a | author=Thauer, R. K. and Shima, S. | title=Biogeochemistry: Methane and microbes | journal = Nature | year = 2006 | volume = 440 | issue = 7086| pages=878–879 | pmid=16612369 }}</ref> MostA methanogensmaioría aredos metanóxenos son produtores [[autotrophicautótrofo]] producerss, butpero thoseos thatque oxidizeoxidan CH<sub>3</sub>COO<sup>-</sup> are(acetato) classedclasifícanse ascomo [[chemotrophquimiótrofo]] insteads.
==Metabolismo fermentativo==
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