NC10 bacteria promoted methane oxidation coupled to chlorate reduction

Area of Science:

• Environmental microbiology
• Biogeochemical cycles
• Anaerobic respiration

Background:

• Methane oxidation is crucial for regulating atmospheric methane levels.
• Coupling methane oxidation to alternative electron acceptors is an area of active research.
• Chlorate reduction offers a potential electron acceptor for anaerobic methane oxidation.

Purpose of the Study:

• To investigate methane oxidation coupled to chlorate reduction (MO-CR) under strictly anaerobic conditions.
• To identify the microbial players and mechanisms involved in MO-CR.
• To compare the efficiency of chlorate versus perchlorate as electron acceptors for methane oxidation.

Main Methods:

• Strictly anaerobic serum bottle incubations.
• Isotope tracing with 13CH4.
• Inhibition tests using C2H2 to target particulate methane monooxygenase (pMMO).
• Real-time quantitative PCR to assess gene expression.
• Detection and enrichment of NC10 bacteria.

Main Results:

• Significant consumption of chlorate (0.35 mM in 20 days) at a higher rate than perchlorate.
• No detectable chlorite production, with high chloride recovery (>89%).
• 13CH4 oxidation to CO2 confirmed, with 77.6% electron recovery.
• Evidence suggests oxygen generated from chlorite disproportionation was used for methane oxidation, supported by pMMO inhibition and gene expression data.
• NC10 bacteria, specifically Candidatus Methylomirabilis, were detected and enriched, correlating with chlorate reduction.

Conclusions:

• Methane oxidation coupled to chlorate reduction is feasible in strictly anaerobic environments.
• NC10 bacteria likely play a key role in MO-CR by performing chlorite disproportionation to generate oxygen for intracellular methane oxidation.
• This study highlights a novel anaerobic methane oxidation pathway with implications for understanding microbial metabolism and biogeochemical cycles.