Anaerobic methane oxidation by a methanogen-sulfate reducer consortium: geochemical evidence and biochemical considerations

Abstract

During the last twenty years, studies employing geochemical models, radiotracers, naturally occurring stable isotopes, and sample incubations have provided compelling evidence in support of anaerobic methane oxidation (Table 1). The first evidence came from geochemical models which show that “concave up” methane concentration profiles observed in many marine sediments can only be accounted for by consumption of methane in anoxic depth intervals. The models have been corroborated by radiotracer experiments which show that ¹⁴CH₄ is converted to ¹⁴CO₂ in anoxic systems. Distributions of naturally occurring stable isotopes provide further evidence of methane oxidation. The presence of ²H- and ¹³C-enriched CH₄ is consistent with kinetic fractionation arising from methane consumption, while the presence of ¹³C-depleted CO₂ implies oxidation of an isotopically “light” substrate (methane). Finally, time-series incubations have shown methane concentration decreases in contained anoxic samples. Given the independent nature of these approaches, the number of investigators, and the wide range of study sites, it is clear that methane is consumed in anoxic environments.