Anaerobic oxidation of methane (AOM) reduces methane emissions from marine ecosystems, but we know little about AOM in freshwater reservoirs. Lake Baikal is the world’s only freshwater reservoir where gas hydrates (GH) are found. Despite that AOM has been demonstrated in deep sediments of Lake Baikal did not reveal methane-oxidizing archaea ANME1, 2, or 3, which are responsible for AOM in marine sediments. A search for representatives Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria (NC10) and Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea (ANME-2d) has been carried out in the different types of Lake Baikal methane enriched sediments. We used different molecular biology methods including high-throughput sequencing and PCR analysis, using 16S rRNA genes as well as different functional genes of AOM (mcrA and pmoA). We found diverse M. oxyfera-like bacteria and M. nitroreducens-like archaea in various geological structures in Lake Baikal (methane seep and mud volcano), which were different from the composition of the discharged fluid. We also considered possible electron acceptors for this process in the sediments of Lake Baikal.

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