TY - JOUR

T1 - Methanotrophs

T2 - Discoveries, Environmental Relevance, and a Perspective on Current and Future Applications

AU - Guerrero-Cruz, Simon

AU - Vaksmaa, Annika

AU - Horn, Marcus A

AU - Niemann, Helge

AU - Pijuan, Maite

AU - Ho, Adrian

N1 - Funding Information: We thank Anniek de Jong and Stefanie Frisch for helpful discussions on methanotrophy and methanogenesis, respectively. Funding. SGC has received funding from the European Union?s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie (Grant no. 892322, project MICROWATER). MP received support from the CERCA program for Generalitat de Catalunya and from the Economy and Knowledge Department of the Catalan Government through a Consolidated Research Group (ICRA-TECH - 2017 SGR 1318). AH received funding from the Deutsche Forschungsgemeinschaft (Grant no. HO6234/1-1). HN and AV received funding from the European Research Council (ERC-CoG Grant no. 772923, project VORTEX).

PY - 2021/5/14

Y1 - 2021/5/14

N2 - Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, co-existence, interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.

AB - Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, co-existence, interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.

KW - anaerobic

KW - application

KW - circular economy

KW - climate change

KW - methane

KW - methanotrophy

KW - microbial ecology

KW - resource recovery

UR - http://www.scopus.com/inward/record.url?scp=85107044473&partnerID=8YFLogxK

U2 - 10.3389/fmicb.2021.678057

DO - 10.3389/fmicb.2021.678057

M3 - Review article

C2 - 34054786

VL - 12

JO - Frontiers in microbiology

JF - Frontiers in microbiology

SN - 1664-302X

M1 - 678057

ER -