Anaerobic Methane Oxidation Mechanisms in Microbial Ecosystems

Anaerobic oxidation of methane (AOM) is a critical microbial process that mitigates methane release from anoxic environments such as marine sediments, freshwater wetlands and deep subseafloor habitats. Central to AOM are specialised archaeal lineages collectively known as anaerobic methanotrophic archaea (ANME), often operating in syntrophic partnership with bacteria or utilising extracellular electron transfer pathways. Methane activation proceeds via a reversed methanogenesis pathway, after which electrons are transferred to terminal electron acceptors including sulfate, nitrate, nitrite or metal oxides. This metabolic versatility underpins the global significance of AOM in controlling greenhouse-gas fluxes and drives biogeochemical cycling in diverse ecosystems.

Research from Nature Portfolio

Recent studies have provided experimental evidence that certain ANME species exploit multi-heme c-type cytochromes to mediate direct electron transfer to extracellular acceptors. In nitrate-adapted enrichment cultures, surface-localised cytochromes facilitate the reduction of iron and electrodes, revealing a modular mechanism for coupling methane oxidation to metal reduction.

Expansive genome reconstructions from hydrothermal Guaymas Basin sediments have uncovered previously unrecognised archaeal and bacterial lineages involved in methane and hydrocarbon turnover. These data point to novel ANME-related clades capable of alkane utilisation and highlight redundancy in core carbon-processing pathways across steep chemical gradients.

Investigations in freshwater wetlands report AOM rates rival marine systems, with activity primarily linked to sulphate reduction yet potentially involving alternative acceptors. Lipid biomarker analyses indicate distinct metabolic pathways in freshwater ANME communities, suggesting that wetland AOM may consume over half of upward methane fluxes, substantially curbing emissions from these traditionally strong sources.

Anaerobic Methane Oxidation Mechanisms in Microbial Ecosystems publication trend

The graph below shows the total number of articles in anaerobic methane oxidation mechanisms in microbial ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Anaerobic oxidation of methane (AOM): Microbial process by which methane is oxidised in the absence of oxygen.

Reverse methanogenesis: Conservation of methanogenic enzymes operating in reverse to oxidise methane to CO₂.

Anaerobic methanotrophic archaea (ANME): Archaeal clades specialised in methane oxidation under anoxic conditions.

Extracellular electron transfer (EET): Mechanism by which microbes transfer electrons to insoluble or distant acceptors outside the cell.

Multi-heme c-type cytochromes: Electron-carrying proteins with multiple haem groups facilitating redox reactions.

Electron acceptor: Chemical species (e.g. sulfate, nitrate, metal oxides) that receives electrons during microbial respiration.

References

1. Anaerobic oxidation of methane: an “active” microbial process. MicrobiologyOpen (2014).
2. Reverse Methanogenesis and Respiration in Methanotrophic Archaea. Archaea (2017).
3. Multi-heme cytochrome-mediated extracellular electron transfer by the anaerobic methanotroph ‘Candidatus Methanoperedens nitroreducens’. Nature Communications (2023).
4. Expansive microbial metabolic versatility and biodiversity in dynamic Guaymas Basin hydrothermal sediments. Nature Communications (2018).
5. High rates of anaerobic methane oxidation in freshwater wetlands reduce potential atmospheric methane emissions. Nature Communications (2015).
6. The majority of microorganisms in gas hydrate-bearing subseafloor sediments ferment macromolecules. Microbiome (2023).
7. Anaerobic methane oxidation coupled to manganese reduction by members of the Methanoperedenaceae. The ISME Journal: Multidisciplinary Journal of Microbial Ecology (2020).
8. Active pathways of anaerobic methane oxidation across contrasting riverbeds. The ISME Journal: Multidisciplinary Journal of Microbial Ecology (2018).