Anaerobic oxidation of methane: an "active" microbial process.

Mengmeng Cui,Hongyan Qi,Xuliang Zhuang,Anzhou Ma,Guoqiang Zhuang

doi:10.1002/mbo3.232

Mengmeng Cui, Hongyan Qi + Show 3 more

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https://doi.org/10.1002/mbo3.232

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Abstract

The anaerobic oxidation of methane (AOM) is an important sink of methane that plays a significant role in global warming. AOM was first found to be coupled with sulfate reduction and mediated by anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). ANME, often forming consortia with SRB, are phylogenetically related to methanogenic archaea. ANME-1 is even able to produce methane. Subsequently, it has been found that AOM can also be coupled with denitrification. The known microbes responsible for this process are Candidatus Methylomirabilis oxyfera (M. oxyfera) and Candidatus Methanoperedens nitroreducens (M. nitroreducens). Candidatus Methylomirabilis oxyfera belongs to the NC10 bacteria, can catalyze nitrite reduction through an “intra-aerobic” pathway, and may catalyze AOM through an aerobic methane oxidation pathway. However, M. nitroreducens, which is affiliated with ANME-2d archaea, may be able to catalyze AOM through the reverse methanogenesis pathway. Moreover, manganese (Mn4+) and iron (Fe3+) can also be used as electron acceptors of AOM. This review summarizes the mechanisms and associated microbes of AOM. It also discusses recent progress in some unclear key issues about AOM, including ANME-1 in hypersaline environments, the effect of oxygen on M. oxyfera, and the relationship of M. nitroreducens with ANME.

Highlights

Methane is the second most abundant greenhouse gas after carbon dioxide (CO2), which accounts for 14% of global greenhouse gas emissions (EPA 2006)
M. nitroreducens, which is affiliated with anaerobic methanotrophs (ANME)-2d archaea, may be able to catalyze anaerobic oxidation of methane (AOM) through the reverse methanogenesis pathway
The mechanism of M-DAMO and the responsible microbes involved still remains unclear, M-DAMO may play an important role in global marine AOM because of the large amounts of manganese and iron provided to continental margins from rivers (Beal et al 2009)

Summary

Introduction

Methane is the second most abundant greenhouse gas after carbon dioxide (CO2), which accounts for 14% of global greenhouse gas emissions (EPA 2006). The M. oxyfera genome contains a complete pmo gene cluster for aerobic methane oxidation (Ettwig et al 2010), but the genetic analyses of different M. oxyfera enrichment cultures showed that they formed a distinct group affiliated with the pmoA genes of aerobic methanotrophs (Luesken et al 2011b). Similar to the sulfate-dependent mode, manganese (Mn4+) (eq 14) and iron (Fe3+) (eq 15) can be used as electron acceptors of AOM in marine methane-seep sediments (Beal et al 2009) This new pathway that involves coupling AOM with metal ion reduction is called M-DAMO. The mechanism of M-DAMO and the responsible microbes involved still remains unclear, M-DAMO may play an important role in global marine AOM because of the large amounts of manganese and iron provided to continental margins from rivers (Beal et al 2009)

Findings

Discussion of Key Issues

Conclusion