Methanotroph: Difference between revisions
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==General== |
==General== |
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Methanotrophs are especially common in or near environments where methane is produced, although some methanotrophs can oxidize [[atmospheric methane]]. Their habitats include wetlands, soils, marshes, rice paddies, landfills, aquatic systems (lakes, oceans, streams) and more. They are of special interest to researchers studying [[global warming]], as they play a significant role in the global methane budget, by reducing the amount of methane emitted to the atmosphere.<ref>{{cite journal |doi= 10.1038/356421a0 |title= Importance of methane-oxidizing bacteria in the methane budget as revealed by the use of a specific inhibitor |year= 1992 | |
Methanotrophs are especially common in or near environments where methane is produced, although some methanotrophs can oxidize [[atmospheric methane]]. Their habitats include wetlands, soils, marshes, rice paddies, landfills, aquatic systems (lakes, oceans, streams) and more. They are of special interest to researchers studying [[global warming]], as they play a significant role in the global methane budget, by reducing the amount of methane emitted to the atmosphere.<ref>{{cite journal |doi= 10.1038/356421a0 |title= Importance of methane-oxidizing bacteria in the methane budget as revealed by the use of a specific inhibitor |year= 1992 |vauthors = Oremland RS, Culbertson CW |journal= Nature |volume= 356 |issue= 6368 |pages= 421–423|bibcode= 1992Natur.356..421O|s2cid= 4234351 }}</ref><ref name=pmid10427012>{{cite journal | vauthors = Holmes AJ, Roslev P, McDonald IR, Iversen N, Henriksen K, Murrell JC | title = Characterization of methanotrophic bacterial populations in soils showing atmospheric methane uptake | journal = Applied and Environmental Microbiology | volume = 65 | issue = 8 | pages = 3312–8 | date = August 1999 | pmid = 10427012 | pmc = 91497 | doi = 10.1128/AEM.65.8.3312-3318.1999 }}</ref> |
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|pmid= 10427012 |
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|year= 1999 |
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|last1= Holmes |
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|first1= AJ |
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|last2= Roslev |
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|first2= P |
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|last3= McDonald |
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|first3= IR |
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|last4= Iversen |
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|first4= N |
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|last5= Henriksen |
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|first5= K |
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|last6= Murrell |
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|first6= JC |
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|title= Characterization of methanotrophic bacterial populations in soils showing atmospheric methane uptake |
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|volume= 65 |
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|issue= 8 |
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|pages= 3312–8 |
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|pmc= 91497 |
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|journal= Applied and Environmental Microbiology |
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|doi= 10.1128/AEM.65.8.3312-3318.1999 |
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}}</ref> |
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Methanotrophy is a special case of [[methylotrophy]], using single-carbon compounds that are more reduced than carbon dioxide. Some methylotrophs, however, can also make use of multi-carbon compounds which differentiates them from methanotrophs that are usually [[growth medium|fastidious]] methane and methanol oxidizers. The only facultative methanotrophs isolated to date are members of the genus ''[[Methylocella silvestris]]''<ref>{{ |
Methanotrophy is a special case of [[methylotrophy]], using single-carbon compounds that are more reduced than carbon dioxide. Some methylotrophs, however, can also make use of multi-carbon compounds which differentiates them from methanotrophs that are usually [[growth medium|fastidious]] methane and methanol oxidizers. The only facultative methanotrophs isolated to date are members of the genus ''[[Methylocella silvestris]]''<ref>{{cite journal | vauthors = Dedysh SN, Knief C, Dunfield PF | title = Methylocella species are facultatively methanotrophic | journal = Journal of Bacteriology | volume = 187 | issue = 13 | pages = 4665–70 | date = July 2005 | pmid = 15968078 | pmc = 1151763 | doi = 10.1128/JB.187.13.4665-4670.2005 | url = https://jb.asm.org/content/187/13/4665 }}</ref><ref>{{cite journal | vauthors = Chen Y, Crombie A, Rahman MT, Dedysh SN, Liesack W, Stott MB, Alam M, Theisen AR, Murrell JC, Dunfield PF | display-authors = 6 | title = Complete genome sequence of the aerobic facultative methanotroph Methylocella silvestris BL2 | journal = Journal of Bacteriology | volume = 192 | issue = 14 | pages = 3840–1 | date = July 2010 | pmid = 20472789 | pmc = 2897342 | doi = 10.1128/JB.00506-10 | url = https://jb.asm.org/content/192/14/3840 }}</ref>, ''[[Methylocapsa aurea]]''<ref>{{cite journal | vauthors = Dunfield PF, Belova SE, Vorob'ev AV, Cornish SL, Dedysh SN | title = Methylocapsa aurea sp. nov., a facultative methanotroph possessing a particulate methane monooxygenase, and emended description of the genus Methylocapsa | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 60 | issue = Pt 11 | pages = 2659–2664 | date = November 2010 | pmid = 20061505 | doi = 10.1099/ijs.0.020149-0 | url = https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.020149-0 }}</ref> and several ''[[Methylocystis]]'' strains<ref>{{cite journal | vauthors = Belova SE, Baani M, Suzina NE, Bodelier PL, Liesack W, Dedysh SN | title = Acetate utilization as a survival strategy of peat-inhabiting Methylocystis spp | journal = Environmental Microbiology Reports | volume = 3 | issue = 1 | pages = 36–46 | date = February 2011 | pmid = 23761229 | doi = 10.1111/j.1758-2229.2010.00180.x | url = http://doi.wiley.com/10.1111/j.1758-2229.2010.00180.x }}</ref>. |
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In functional terms, methanotrophs are referred to as methane-oxidizing bacteria, however, methane-oxidizing bacteria encompass other organisms that are not regarded as sole methanotrophs. For this reason methane-oxidizing bacteria have been separated into subgroups: methane-assimilating bacteria (MAB) groups, the methanotrophs, and autotrophic [[ammonia-oxidizing bacteria]] (AAOB) which cooxidize methane.<ref name=pmid10427012/> |
In functional terms, methanotrophs are referred to as methane-oxidizing bacteria, however, methane-oxidizing bacteria encompass other organisms that are not regarded as sole methanotrophs. For this reason methane-oxidizing bacteria have been separated into subgroups: methane-assimilating bacteria (MAB) groups, the methanotrophs, and autotrophic [[ammonia-oxidizing bacteria]] (AAOB) which cooxidize methane.<ref name=pmid10427012/> |
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===Aerobic methanotrophs=== |
===Aerobic methanotrophs=== |
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Under aerobic conditions, methanotrophs combine [[oxygen]] and [[methane]] to form [[formaldehyde]], which is then incorporated into organic compounds via the serine pathway or the ribulose monophosphate (RuMP) pathway, and [Carbon dioxide], which is released. Type I and type X methanotrophs are part of the [[Gammaproteobacteria]] and they use the RuMP pathway to assimilate carbon. Type II methanotrophs are part of the [[Alphaproteobacteria]] and utilize the serine pathway of carbon assimilation. They also characteristically have a system of internal membranes within which methane [[redox|oxidation]] occurs. Methanotrophs in [[Gammaproteobacteria]] are known from family ''[[Methylococcaceae]]''.<ref>{{ |
Under aerobic conditions, methanotrophs combine [[oxygen]] and [[methane]] to form [[formaldehyde]], which is then incorporated into organic compounds via the serine pathway or the ribulose monophosphate (RuMP) pathway, and [Carbon dioxide], which is released. Type I and type X methanotrophs are part of the [[Gammaproteobacteria]] and they use the RuMP pathway to assimilate carbon. Type II methanotrophs are part of the [[Alphaproteobacteria]] and utilize the serine pathway of carbon assimilation. They also characteristically have a system of internal membranes within which methane [[redox|oxidation]] occurs. Methanotrophs in [[Gammaproteobacteria]] are known from family ''[[Methylococcaceae]]''.<ref>{{cite book | vauthors = Stein LY, Roy R, Dunfield PF | chapter = Aerobic Methanotrophy and Nitrification: Processes and Connections|date=2012-04-16|url=http://doi.wiley.com/10.1002/9780470015902.a0022213| title = eLS|pages=a0022213 |place=Chichester, UK|publisher=John Wiley & Sons, Ltd|language=en|doi=10.1002/9780470015902.a0022213|isbn=978-0-470-01617-6|access-date=2021-01-17}}</ref> Methanotrophs from [[Alphaproteobacteria]] are found in families ''[[Methylocystaceae]]'' and ''[[Beijerinckiaceae]]''. |
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Aerobic methanotrophs are also known from the [[Methylacidiphilaceae]] (phylum [[Verrucomicrobia]]).<ref>{{ |
Aerobic methanotrophs are also known from the [[Methylacidiphilaceae]] (phylum [[Verrucomicrobia]]).<ref>{{cite journal | vauthors = Op den Camp HJ, Islam T, Stott MB, Harhangi HR, Hynes A, Schouten S, Jetten MS, Birkeland NK, Pol A, Dunfield PF | display-authors = 6 | title = Environmental, genomic and taxonomic perspectives on methanotrophic Verrucomicrobia | journal = Environmental Microbiology Reports | volume = 1 | issue = 5 | pages = 293–306 | date = October 2009 | pmid = 23765882 | doi = 10.1111/j.1758-2229.2009.00022.x | url = http://doi.wiley.com/10.1111/j.1758-2229.2009.00022.x }}</ref> In contrast to [[Gammaproteobacteria]] and [[Alphaproteobacteria]], methanotrophs in the phylum [[Verrucomicrobia]] are [[mixotroph]]s.<ref>{{cite journal | vauthors = Carere CR, Hards K, Houghton KM, Power JF, McDonald B, Collet C, Gapes DJ, Sparling R, Boyd ES, Cook GM, Greening C, Stott MB | display-authors = 6 | title = Mixotrophy drives niche expansion of verrucomicrobial methanotrophs | journal = The ISME Journal | volume = 11 | issue = 11 | pages = 2599–2610 | date = November 2017 | pmid = 28777381 | pmc = 5649168 | doi = 10.1038/ismej.2017.112 | url = http://www.nature.com/articles/ismej2017112 }}</ref><ref>{{cite journal | vauthors = Sharp CE, Stott MB, Dunfield PF | title = Detection of autotrophic verrucomicrobial methanotrophs in a geothermal environment using stable isotope probing | journal = Frontiers in Microbiology | volume = 3 | pages = 303 | date = 2012 | pmid = 22912630 | pmc = 3421453 | doi = 10.3389/fmicb.2012.00303 | url = http://journal.frontiersin.org/article/10.3389/fmicb.2012.00303/abstract }}</ref> In 2021 bacterial [[Binning (metagenomics)|bin]] from the phylum [[Gemmatimonadetes]] called ''Candidatus'' Methylotropicum kingii showing aerobic methanotrophy was discovered thus suggesting methanotrophy to be present in the four bacterial phyla.<ref>{{cite journal | vauthors = Bay SK, Dong X, Bradley JA, Leung PM, Grinter R, Jirapanjawat T, Arndt SK, Cook PL, LaRowe DE, Nauer PA, Chiri E, Greening C | display-authors = 6 | title = Trace gas oxidizers are widespread and active members of soil microbial communities | journal = Nature Microbiology | pages = 1–11 | date = January 2021 | pmid = 33398096 | doi = 10.1038/s41564-020-00811-w | url = https://www.nature.com/articles/s41564-020-00811-w }}</ref> |
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No aerobic methanotrophic [[archaea]] are known. |
No aerobic methanotrophic [[archaea]] are known. |
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===Anaerobic methanotrophs=== |
===Anaerobic methanotrophs=== |
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Under anoxic conditions, methanotrophs use different [[electron acceptor]]s for methane oxidation. This can happen in [[anoxic waters|anoxic]] habitats such as marine or lake [[sediments]], [[oxygen minimum zone]]s, anoxic water columns, rice paddies and soils. Some specific methanotrophs can reduce nitrate or nitrite, and couple that to methane oxidation. Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing [[archaea]] and [[sulfate-reducing bacteria]]. This type of [[anaerobic oxidation of methane]] (AOM) mainly occurs in anoxic marine sediments. The exact mechanism behind this is still a topic of debate but the most widely accepted theory is that the archaea use the reversed [[methanogenesis]] pathway to produce carbon dioxide and another, unknown substance. This unknown intermediate is then used by the sulfate-reducing bacteria to gain energy from the reduction of sulfate to [[hydrogen sulfide]]. The anaerobic methanotrophs are not related to the known aerobic methanotrophs; the closest cultured relative to the anaerobic methanotrophs are the [[methanogen]]s in the [[order (biology)|order]] [[Methanosarcinales]].<ref>{{cite journal | |
Under anoxic conditions, methanotrophs use different [[electron acceptor]]s for methane oxidation. This can happen in [[anoxic waters|anoxic]] habitats such as marine or lake [[sediments]], [[oxygen minimum zone]]s, anoxic water columns, rice paddies and soils. Some specific methanotrophs can reduce nitrate or nitrite, and couple that to methane oxidation. Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing [[archaea]] and [[sulfate-reducing bacteria]]. This type of [[anaerobic oxidation of methane]] (AOM) mainly occurs in anoxic marine sediments. The exact mechanism behind this is still a topic of debate but the most widely accepted theory is that the archaea use the reversed [[methanogenesis]] pathway to produce carbon dioxide and another, unknown substance. This unknown intermediate is then used by the sulfate-reducing bacteria to gain energy from the reduction of sulfate to [[hydrogen sulfide]]. The anaerobic methanotrophs are not related to the known aerobic methanotrophs; the closest cultured relative to the anaerobic methanotrophs are the [[methanogen]]s in the [[order (biology)|order]] [[Methanosarcinales]].<ref>{{cite journal | vauthors = Boetius A, Ravenschlag K, Schubert CJ, Rickert D, Widdel F, Gieseke A, Amann R, Jørgensen BB, Witte U, Pfannkuche O | display-authors = 6 | title = A marine microbial consortium apparently mediating anaerobic oxidation of methane | journal = Nature | volume = 407 | issue = 6804 | pages = 623–6 | date = October 2000 | pmid = 11034209 | doi = 10.1038/35036572 | url = https://www.researchgate.net/publication/12290603 | url-access = registration | s2cid = 205009562 | author1-link = Antje Boetius }}</ref> |
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Metal-oxides, such as manganese and iron, can also be used as terminal electron acceptors by ANME. For this, no consortium is needed. ANME shuttle electrons directly to the [[abiotic]] particles, which get reduced chemically.<ref>{{cite journal | |
Metal-oxides, such as manganese and iron, can also be used as terminal electron acceptors by ANME. For this, no consortium is needed. ANME shuttle electrons directly to the [[abiotic]] particles, which get reduced chemically.<ref>{{cite journal | vauthors = Scheller S, Yu H, Chadwick GL, McGlynn SE, Orphan VJ | title = Artificial electron acceptors decouple archaeal methane oxidation from sulfate reduction | journal = Science | volume = 351 | issue = 6274 | pages = 703–7 | date = February 2016 | pmid = 26912857 | doi = 10.1126/science.aad7154 | url = https://authors.library.caltech.edu/64490/2/aad7154-Scheller-SM.pdf | s2cid = 41009096 }}</ref> |
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In some cases, [[Cellular respiration#Aerobic respiration|aerobic]] methane oxidation can take place in anoxic (no oxygen) environments. ''Candidatus'' Methylomirabilis oxyfera belongs to the [[NC10 phylum|phylum NC10]] bacteria, and can catalyze nitrite reduction through an "intra-aerobic" pathway, in which internally produced oxygen is used to oxidise methane.<ref name="Ettwig2010" /><ref>{{ |
In some cases, [[Cellular respiration#Aerobic respiration|aerobic]] methane oxidation can take place in anoxic (no oxygen) environments. ''Candidatus'' Methylomirabilis oxyfera belongs to the [[NC10 phylum|phylum NC10]] bacteria, and can catalyze nitrite reduction through an "intra-aerobic" pathway, in which internally produced oxygen is used to oxidise methane.<ref name="Ettwig2010" /><ref>{{cite journal | vauthors = Zhu B, van Dijk G, Fritz C, Smolders AJ, Pol A, Jetten MS, Ettwig KF | title = Anaerobic oxidization of methane in a minerotrophic peatland: enrichment of nitrite-dependent methane-oxidizing bacteria | journal = Applied and Environmental Microbiology | volume = 78 | issue = 24 | pages = 8657–65 | date = December 2012 | pmid = 23042166 | pmc = 3502929 | doi = 10.1128/AEM.02102-12 | url = http://aem.asm.org/lookup/doi/10.1128/AEM.02102-12 }}</ref> In clear water lakes, methanotrophs can live in the anoxic water column, but receive oxygen from [[Photosynthesis|photosynthetic]] organisms, that they then directly consume to oxidise methane aerobically.<ref>{{cite journal | vauthors = Milucka J, Kirf M, Lu L, Krupke A, Lam P, Littmann S, Kuypers MM, Schubert CJ | display-authors = 6 | title = Methane oxidation coupled to oxygenic photosynthesis in anoxic waters | journal = The ISME Journal | volume = 9 | issue = 9 | pages = 1991–2002 | date = September 2015 | pmid = 25679533 | pmc = 4542029 | doi = 10.1038/ismej.2015.12 }}</ref> |
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===Special methanotroph species=== |
===Special methanotroph species=== |
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''[[Methylococcus capsulatus]]'' is utilised to produce animal feed from natural gas.<ref>{{Cite news|url=https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/|title=Food made from natural gas will soon feed farm animals – and us| |
''[[Methylococcus capsulatus]]'' is utilised to produce animal feed from natural gas.<ref>{{Cite news|url=https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/|title=Food made from natural gas will soon feed farm animals – and us| vauthors = Le Page M |date=2016-11-19|newspaper=New Scientist|language=en-US|access-date=2016-12-11}}</ref> |
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In 2010 a new bacterium ''Candidatus'' Methylomirabilis oxyfera from the [[NC10 phylum|phylum NC10]] was identified that can couple the [[anaerobic oxidation of methane]] to nitrite reduction without the need for a [[syntrophy|syntrophic]] partner.<ref name=Ettwig2010>{{cite journal |
In 2010 a new bacterium ''Candidatus'' Methylomirabilis oxyfera from the [[NC10 phylum|phylum NC10]] was identified that can couple the [[anaerobic oxidation of methane]] to nitrite reduction without the need for a [[syntrophy|syntrophic]] partner.<ref name=Ettwig2010>{{cite journal | vauthors = Ettwig KF, Butler MK, Le Paslier D, Pelletier E, Mangenot S, Kuypers MM, Schreiber F, Dutilh BE, Zedelius J, de Beer D, Gloerich J, Wessels HJ, van Alen T, Luesken F, Wu ML, van de Pas-Schoonen KT, Op den Camp HJ, Janssen-Megens EM, Francoijs KJ, Stunnenberg H, Weissenbach J, Jetten MS, Strous M | display-authors = 6 | title = Nitrite-driven anaerobic methane oxidation by oxygenic bacteria | journal = Nature | volume = 464 | issue = 7288 | pages = 543–8 | date = March 2010 | pmid = 20336137 | doi = 10.1038/nature08883 | url = https://hal-cea.archives-ouvertes.fr/cea-00907649/file/Ett.pdf | s2cid = 205220000 | bibcode = 2010Natur.464..543E }}</ref> Based on the studies of Ettwig et al.,<ref name=Ettwig2010/> it is believed that ''M. oxyfera'' oxidizes methane anaerobically by utilizing the oxygen produced internally from the [[dismutation]] of [[nitric oxide]] into nitrogen and oxygen gas. |
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|last1= Ettwig |first1= K. F. |
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|last2= Butler |first2= M. K. |
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|last3= Le Paslier |first3= D. |
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|last4= Pelletier |first4= E. |
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|last5= Mangenot |first5= S. |
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|last6= Kuypers |first6= M. M. M. |
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|last7= Schreiber |first7= F. |
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|last8= Dutilh |first8= B. E. |
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|last9= Zedelius |first9= J. |
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|last10= De Beer |
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|doi= 10.1038/nature08883 |first10= D. |
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|last11= Gloerich |first11= J. |
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|last12= Wessels |first12= H. J. C. T. |
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|last13= Van Alen |first13= T. |
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|last14= Luesken |first14= F. |
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|last15= Wu |first15= M. L. |
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|last16= Van De Pas-Schoonen |first16= K. T. |
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|last17= Op Den Camp |first17= H. J. M. |
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|last18= Janssen-Megens |first18= E. M. |
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|last19= Francoijs |first19= K. J. |
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|last20= Stunnenberg |first20= H. |
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|last21= Weissenbach |first21= J. |
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|last22= Jetten |first22= M. S. M. |
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|last23= Strous |first23= M. |
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|title= Nitrite-driven anaerobic methane oxidation by oxygenic bacteria |
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|journal= Nature |
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|volume= 464 |
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|issue= 7288 |
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|pages= 543–548 |
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|year= 2010 |
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|pmid= 20336137 |
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|bibcode= 2010Natur.464..543E|s2cid= 205220000 |
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|url= https://hal-cea.archives-ouvertes.fr/cea-00907649/file/Ett.pdf |
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}}</ref> Based on the studies of Ettwig et al.,<ref name=Ettwig2010/> it is believed that ''M. oxyfera'' oxidizes methane anaerobically by utilizing the oxygen produced internally from the [[dismutation]] of [[nitric oxide]] into nitrogen and oxygen gas. |
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== Methanotroph Taxonomy == |
== Methanotroph Taxonomy == |
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Many methanotrophic cultures have been isolated and formally characterized over the past 4 decades, starting with the classical study of Whittenbury (Whittenbury et al., 1970). Currently,18 genera of cultivated aerobic methanotrophic ''Gammaproteobacteria'' and 5 genera of ''Alphaproteobacteria'' are known, represented by approx. 60 different species.<ref>{{ |
Many methanotrophic cultures have been isolated and formally characterized over the past 4 decades, starting with the classical study of Whittenbury (Whittenbury et al., 1970). Currently,18 genera of cultivated aerobic methanotrophic ''Gammaproteobacteria'' and 5 genera of ''Alphaproteobacteria'' are known, represented by approx. 60 different species.<ref>{{cite journal | vauthors = Orata FD, Meier-Kolthoff JP, Sauvageau D, Stein LY | title = Phylogenomic Analysis of the Gammaproteobacterial Methanotrophs (Order <i>Methylococcales</i>) Calls for the Reclassification of Members at the Genus and Species Levels | journal = Frontiers in Microbiology | volume = 9 | pages = 3162 | date = 2018 | pmid = 30631317 | pmc = 6315193 | doi = 10.3389/fmicb.2018.03162 }}</ref> |
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== Methane Oxidation by Methanotrophs == |
== Methane Oxidation by Methanotrophs == |
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Methanotrophs oxidize methane by first initiating reduction of an oxygen atom to H<sub>2</sub>O<sub>2 </sub>and transformation of methane to CH<sub>3</sub>OH using [[Methane monooxygenase|methane monooxygenases (MMOs)]].<ref name=pmid8801441>{{cite journal |
Methanotrophs oxidize methane by first initiating reduction of an oxygen atom to H<sub>2</sub>O<sub>2 </sub>and transformation of methane to CH<sub>3</sub>OH using [[Methane monooxygenase|methane monooxygenases (MMOs)]].<ref name=pmid8801441>{{cite journal | vauthors = Hanson RS, Hanson TE | title = Methanotrophic bacteria | journal = Microbiological Reviews | volume = 60 | issue = 2 | pages = 439–71 | date = June 1996 | pmid = 8801441 | pmc = 239451 | doi = 10.1128/MMBR.60.2.439-471.1996 }}</ref> Furthermore, two types of MMO have been isolated from methanotrophs: soluble methane monooxygenase (sMMO) and [[Methane monooxygenase (particulate)|particulate methane monooxygenase (pMMO)]]. |
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|last1= Hanson |first1= R. S. |
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|last2= Hanson |first2= T. E. |
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|title= Methanotrophic bacteria |
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|journal= Microbiological Reviews |
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|volume= 60 |
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|issue= 2 |
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|pages= 439–471 |
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|year= 1996 |
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|pmid= 8801441 |
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|pmc= 239451 |
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|doi= 10.1128/MMBR.60.2.439-471.1996 |
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}}</ref> Furthermore, two types of MMO have been isolated from methanotrophs: soluble methane monooxygenase (sMMO) and [[Methane monooxygenase (particulate)|particulate methane monooxygenase (pMMO)]]. |
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Cells containing pMMO have demonstrated higher growth capabilities and higher affinity for methane than sMMO containing cells.<ref name="pmid8801441" /> It is suspected that copper ions may play a key role in both pMMO regulation and the enzyme catalysis, thus limiting pMMO cells to more copper-rich environments than sMMO producing cells.<ref>{{cite journal |
Cells containing pMMO have demonstrated higher growth capabilities and higher affinity for methane than sMMO containing cells.<ref name="pmid8801441" /> It is suspected that copper ions may play a key role in both pMMO regulation and the enzyme catalysis, thus limiting pMMO cells to more copper-rich environments than sMMO producing cells.<ref>{{cite journal | vauthors = Lieberman RL, Rosenzweig AC | title = Biological methane oxidation: regulation, biochemistry, and active site structure of particulate methane monooxygenase | journal = Critical Reviews in Biochemistry and Molecular Biology | volume = 39 | issue = 3 | pages = 147–64 | year = 2004 | pmid = 15596549 | doi = 10.1080/10409230490475507 | s2cid = 21628195 }}</ref> |
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|last1= Lieberman |first1= R. L. |
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|last2= Rosenzweig |first2= A. C. |
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|doi= 10.1080/10409230490475507 |
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|title= Biological Methane Oxidation: Regulation, Biochemistry, and Active Site Structure of Particulate Methane Monooxygenase |
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|journal= Critical Reviews in Biochemistry and Molecular Biology |
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|volume= 39 |
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|issue= 3 |
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|pages= 147–164 |
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|year= 2004 |
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|pmid= 15596549 |
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|s2cid= 21628195 |
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}}</ref> |
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==References== |
== References == |
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{{reflist|2}} |
{{reflist|2}} |
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==External links== |
== External links == |
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*[[Anaerobic oxidation of methane]] |
*[[Anaerobic oxidation of methane]] |
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*[http://www.gns.cri.nz/Home/News-and-Events/Media-Releases/Methane-eating-bug Methane-Eating Bug Holds Promise For Cutting Greenhouse Gas]. Media Release, GNS Science, New Zealand |
*[http://www.gns.cri.nz/Home/News-and-Events/Media-Releases/Methane-eating-bug Methane-Eating Bug Holds Promise For Cutting Greenhouse Gas]. Media Release, GNS Science, New Zealand |
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Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and energy. They can be either bacteria or archaea and can grow aerobically or anaerobically, and require single-carbon compounds to survive.
General
Methanotrophs are especially common in or near environments where methane is produced, although some methanotrophs can oxidize atmospheric methane. Their habitats include wetlands, soils, marshes, rice paddies, landfills, aquatic systems (lakes, oceans, streams) and more. They are of special interest to researchers studying global warming, as they play a significant role in the global methane budget, by reducing the amount of methane emitted to the atmosphere.[1][2]
Methanotrophy is a special case of methylotrophy, using single-carbon compounds that are more reduced than carbon dioxide. Some methylotrophs, however, can also make use of multi-carbon compounds which differentiates them from methanotrophs that are usually fastidious methane and methanol oxidizers. The only facultative methanotrophs isolated to date are members of the genus Methylocella silvestris[3][4], Methylocapsa aurea[5] and several Methylocystis strains[6].
In functional terms, methanotrophs are referred to as methane-oxidizing bacteria, however, methane-oxidizing bacteria encompass other organisms that are not regarded as sole methanotrophs. For this reason methane-oxidizing bacteria have been separated into subgroups: methane-assimilating bacteria (MAB) groups, the methanotrophs, and autotrophic ammonia-oxidizing bacteria (AAOB) which cooxidize methane.[2]
Methanotroph classification
Methantrophs can be either bacteria or archaea. Which methanotroph species is present, is mainly determined by the availability of electron acceptors. Many types of methane oxidizing bacteria (MOB) are known. Differences in the method of formaldehyde fixation and membrane structure divide these bacterial methanotrophs into several groups. Among the methanotrophic archaea, several subgroups are determined.
Aerobic methanotrophs
Under aerobic conditions, methanotrophs combine oxygen and methane to form formaldehyde, which is then incorporated into organic compounds via the serine pathway or the ribulose monophosphate (RuMP) pathway, and [Carbon dioxide], which is released. Type I and type X methanotrophs are part of the Gammaproteobacteria and they use the RuMP pathway to assimilate carbon. Type II methanotrophs are part of the Alphaproteobacteria and utilize the serine pathway of carbon assimilation. They also characteristically have a system of internal membranes within which methane oxidation occurs. Methanotrophs in Gammaproteobacteria are known from family Methylococcaceae.[7] Methanotrophs from Alphaproteobacteria are found in families Methylocystaceae and Beijerinckiaceae.
Aerobic methanotrophs are also known from the Methylacidiphilaceae (phylum Verrucomicrobia).[8] In contrast to Gammaproteobacteria and Alphaproteobacteria, methanotrophs in the phylum Verrucomicrobia are mixotrophs.[9][10] In 2021 bacterial bin from the phylum Gemmatimonadetes called Candidatus Methylotropicum kingii showing aerobic methanotrophy was discovered thus suggesting methanotrophy to be present in the four bacterial phyla.[11]
No aerobic methanotrophic archaea are known.
Anaerobic methanotrophs
Under anoxic conditions, methanotrophs use different electron acceptors for methane oxidation. This can happen in anoxic habitats such as marine or lake sediments, oxygen minimum zones, anoxic water columns, rice paddies and soils. Some specific methanotrophs can reduce nitrate or nitrite, and couple that to methane oxidation. Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing archaea and sulfate-reducing bacteria. This type of anaerobic oxidation of methane (AOM) mainly occurs in anoxic marine sediments. The exact mechanism behind this is still a topic of debate but the most widely accepted theory is that the archaea use the reversed methanogenesis pathway to produce carbon dioxide and another, unknown substance. This unknown intermediate is then used by the sulfate-reducing bacteria to gain energy from the reduction of sulfate to hydrogen sulfide. The anaerobic methanotrophs are not related to the known aerobic methanotrophs; the closest cultured relative to the anaerobic methanotrophs are the methanogens in the order Methanosarcinales.[12] Metal-oxides, such as manganese and iron, can also be used as terminal electron acceptors by ANME. For this, no consortium is needed. ANME shuttle electrons directly to the abiotic particles, which get reduced chemically.[13]
In some cases, aerobic methane oxidation can take place in anoxic (no oxygen) environments. Candidatus Methylomirabilis oxyfera belongs to the phylum NC10 bacteria, and can catalyze nitrite reduction through an "intra-aerobic" pathway, in which internally produced oxygen is used to oxidise methane.[14][15] In clear water lakes, methanotrophs can live in the anoxic water column, but receive oxygen from photosynthetic organisms, that they then directly consume to oxidise methane aerobically.[16]
Special methanotroph species
Methylococcus capsulatus is utilised to produce animal feed from natural gas.[17]
In 2010 a new bacterium Candidatus Methylomirabilis oxyfera from the phylum NC10 was identified that can couple the anaerobic oxidation of methane to nitrite reduction without the need for a syntrophic partner.[14] Based on the studies of Ettwig et al.,[14] it is believed that M. oxyfera oxidizes methane anaerobically by utilizing the oxygen produced internally from the dismutation of nitric oxide into nitrogen and oxygen gas.
Methanotroph Taxonomy
Many methanotrophic cultures have been isolated and formally characterized over the past 4 decades, starting with the classical study of Whittenbury (Whittenbury et al., 1970). Currently,18 genera of cultivated aerobic methanotrophic Gammaproteobacteria and 5 genera of Alphaproteobacteria are known, represented by approx. 60 different species.[18]
Methane Oxidation by Methanotrophs
RuMP pathway in type I methanotrophs
Serine pathway in type II methanotrophs
Methanotrophs oxidize methane by first initiating reduction of an oxygen atom to H2O2 and transformation of methane to CH3OH using methane monooxygenases (MMOs).[19] Furthermore, two types of MMO have been isolated from methanotrophs: soluble methane monooxygenase (sMMO) and particulate methane monooxygenase (pMMO).
Cells containing pMMO have demonstrated higher growth capabilities and higher affinity for methane than sMMO containing cells.[19] It is suspected that copper ions may play a key role in both pMMO regulation and the enzyme catalysis, thus limiting pMMO cells to more copper-rich environments than sMMO producing cells.[20]
References
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- ^ Dedysh SN, Knief C, Dunfield PF (July 2005). "Methylocella species are facultatively methanotrophic". Journal of Bacteriology. 187 (13): 4665–70. doi:10.1128/JB.187.13.4665-4670.2005. PMC 1151763. PMID 15968078.
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- ^ Stein LY, Roy R, Dunfield PF (2012-04-16). "Aerobic Methanotrophy and Nitrification: Processes and Connections". eLS. Chichester, UK: John Wiley & Sons, Ltd. pp. a0022213. doi:10.1002/9780470015902.a0022213. ISBN 978-0-470-01617-6. Retrieved 2021-01-17.
- ^ Op den Camp HJ, Islam T, Stott MB, Harhangi HR, Hynes A, Schouten S, et al. (October 2009). "Environmental, genomic and taxonomic perspectives on methanotrophic Verrucomicrobia". Environmental Microbiology Reports. 1 (5): 293–306. doi:10.1111/j.1758-2229.2009.00022.x. PMID 23765882.
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{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Bay SK, Dong X, Bradley JA, Leung PM, Grinter R, Jirapanjawat T, et al. (January 2021). "Trace gas oxidizers are widespread and active members of soil microbial communities". Nature Microbiology: 1–11. doi:10.1038/s41564-020-00811-w. PMID 33398096.
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- ^ Orata FD, Meier-Kolthoff JP, Sauvageau D, Stein LY (2018). "Phylogenomic Analysis of the Gammaproteobacterial Methanotrophs (Order Methylococcales) Calls for the Reclassification of Members at the Genus and Species Levels". Frontiers in Microbiology. 9: 3162. doi:10.3389/fmicb.2018.03162. PMC 6315193. PMID 30631317.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b Hanson RS, Hanson TE (June 1996). "Methanotrophic bacteria". Microbiological Reviews. 60 (2): 439–71. doi:10.1128/MMBR.60.2.439-471.1996. PMC 239451. PMID 8801441.
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External links
- Anaerobic oxidation of methane
- Methane-Eating Bug Holds Promise For Cutting Greenhouse Gas. Media Release, GNS Science, New Zealand