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A pathway for biological methane production using bacterial iron-only nitrogenase
Yanning Zheng1, Derek F Harris2, Zheng Yu3
1Department of Microbiology, University of Washington, Seattle, WA, USA.
Nature Microbiology
|January 17, 2018
Summary
Iron-iron nitrogenase, an enzyme found in bacteria, can convert carbon dioxide into methane (CH4). This microbial methane production supports the growth of other methane-consuming bacteria and influences microbial communities.
Area of Science:
- Biochemistry
- Microbiology
- Environmental Science
Background:
- Methane (CH4) is a potent greenhouse gas primarily produced by archaea through complex methanogenesis pathways.
- Microbial activity accounts for the formation and consumption of at least one billion tonnes of CH4 annually.
- Understanding alternative sources of biological methane production is crucial for environmental and ecological studies.
Purpose of the Study:
- To investigate the potential of iron-iron (Fe-only) nitrogenase from Rhodopseudomonas palustris to produce methane (CH4) from carbon dioxide (CO2).
- To determine if Fe-only nitrogenase can mediate the conversion of CO2 to CH4 in a single enzymatic step.
- To assess the ecological significance of CH4 production by Fe-only nitrogenase in microbial communities.
Main Methods:
- Purification of wild-type iron-iron (Fe-only) nitrogenase from Rhodopseudomonas palustris.
- Enzymatic assays to measure the reduction of CO2, N2, and protons by Fe-only nitrogenase.
- Co-culture experiments with R. palustris expressing Fe-only nitrogenase and a methane-utilizing Methylomonas strain.
- Genomic analysis to identify the prevalence of Fe-only nitrogenase genes in diverse microorganisms.
Main Results:
- Fe-only nitrogenase was found to reduce CO2, N2, and protons to yield CH4, ammonia (NH3), and hydrogen (H2) in a single enzymatic step.
- While CH4 production was low in purified enzyme preparations, it was sufficient to support the growth of a co-cultured methane-utilizing bacterium.
- CH4 production was observed in other nitrogen-fixing bacteria expressing Fe-only nitrogenase, indicating a general property of the enzyme.
- Fe-only nitrogenase genes are encoded in 9% of diverse nitrogen-fixing microorganisms.
Conclusions:
- Wild-type iron-iron nitrogenase possesses the capability to produce methane (CH4) from carbon dioxide (CO2).
- Microbial methane production via Fe-only nitrogenase can influence inter-species microbial interactions and community dynamics.
- The widespread presence of Fe-only nitrogenase suggests a significant, yet underappreciated, contribution to biological methane cycling.
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