Anaerobic oxidation of methane by aerobic methanotrophs in sub-Arctic lake sediments.

Anaerobic oxidation of methane (AOM) is a biological process that plays an important role in reducing the CH4 emissions from a wide range of ecosystems. Arctic and sub-Arctic lakes are recognized as significant contributors to global methane (CH4) emission, since CH4 production is increasing as permafrost thaws and provides fuels for methanogenesis. Methanotrophy, including AOM, is critical to reducing CH4 emissions. The identity, activity, and metabolic processes of anaerobic methane oxidizers are poorly understood, yet this information is critical to understanding CH4 cycling and ultimately to predicting future CH4 emissions. This study sought to identify the microorganisms involved in AOM in sub-Arctic lake sediments using DNA- and phospholipid-fatty acid (PLFA)- based stable isotope probing. Results indicated that aerobic methanotrophs belonging to the genus Methylobacter assimilate carbon from CH4, either directly or indirectly. Other organisms that were found, in minor proportions, to assimilate CH4-derived carbon were methylotrophs and iron reducers, which might indicate the flow of CH4-derived carbon from anaerobic methanotrophs into the broader microbial community. While various other taxa have been reported in the literature to anaerobically oxidize methane in various environments (e.g. ANME-type archaea and Methylomirabilis Oxyfera), this report directly suggest that Methylobacter can perform this function, expanding our understanding of CH4 oxidation in anaerobic lake sediments.