Methane oxidation and its coupled electron-sink reactions in ruminal fluid.

AIMS: This study was conducted to investigate the occurrence of methane oxidation in the rumen, and to identify the electron-sink reaction coupled to the oxidation if it occurred. METHODS AND RESULTS: Mixed ruminal microbes taken from sheep were incubated with 13CH4. Oxidation of methane, estimated from the flux of 13C to CO2 and microbial cells, occurred, but represented only 0.2-0.5% of the methane produced. Methane oxidation was suppressed by the presence of oxygen, and was also inhibited by 2-bromoethane-sulphonate, and molybdate, but not by tungstate. CONCLUSION, SIGNIFICANCE AND IMPACT OF THE STUDY: Methane could be oxidized anaerobically in the rumen by reverse methanogenesis in consort with sulphate reduction.