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.

At the site of natural ingress of oil, microbial diversity in the Central Baikal bottom sediments differing in the chemical composition of pore waters was studied by molecular biological techniques....

Using massively parallel sequencing (the Roche 454 platform) we have studied the diversity of archaeal 16S rRNA gene sequences in oxic and anoxic sediments at six sites in Lake Baikal with oil- and gas-bearing fluids discharge. Archaeal communities appeared to be represented mainly by five phyla: Euryarchaeota, Crenarchaeota, Thaumarchaeota, Bathyarchaeota (miscellaneous Crenarchaeotic group), and Woesearchaeota (deep sea hydrothermal vent group 6). Among them we detected sequences of methanogens of the orders Methanomicrobiales, Methanosarsinales, Methanococcales, as well as representatives of the following uncultured archaeal lineages: Group C3, Marine Benthic Group D, and Terrestrial Miscellaneous Group. We have also identified sequences of ammonia-oxidizing archaea of the phyla Crenarchaeota and Thaumarchaeota. Phylogenetic analysis showed the presence ANME-2d-related sequences. However, the analysis of mcrA genes libraries has not revealed typical representatives of ANME groups. Comparison of amplicon libraries 16S rRNA gene fragments from different samples proved the widespread presence of previously detected Baikal archaeal lineages, which are members of the phylum Crenarchaeota and Thaumarchaeota (formerly Group C3 of Crenarchaeota).

Background: Rhodococci are bacteria able to degrade a wide range of hydrocarbons, including the alkanes present in crude oil, due to alk genes in their genomes. Findings: Genome sequencing of DNA from Rhodococcus erythropolis strain 4 (obtained from a deep-water bitumen mound) revealed four alk genes, and the predicted amino acid sequences coded by these genes were highly conserved, having sections up to 11 amino acid residues. Conclusions: Obtained four genes from Rhodococcus erythropolis were similar to corresponding genes from other bacteria collected from other environments, including marine sources. This indicated a large-scale horizontal alk gene transfer between bacteria from different subgenera.

We analyzed the amplicons of the 16S rRNA genes and assembled metagenome-assembled genomes (MAGs) of the enrichment culture from the Fe-Mn layer to have an insight into the diversity and metabolic potential of microbial communities from sediments of two sites in the northern basin of Lake Baikal. Organotrophic Chloroflexota, Actionobacteriota, and Acidobacteriota, as well as aerobic and anaerobic participants of the methane cycle (Methylococcales and Methylomirabilota, respectively), dominated the communities of the surface layers. With depth, one of the cores showed a decrease in the proportion of the Chloroflexota and Acidobacteriota members and a substantial increase in the sequences of the phylum Firmicutes. The proportion of the Desulfobacteriota and Thermodesulfovibronia (Nitrospirota) increased in another core. The composition of archaeal communities was similar between the investigated sites and differed in depth. Members of ammonia-oxidizing archaea (Nitrososphaeria) predominated in the surface sediments, with an increase in anaerobic methanotrophs (Methanoperedenaceae) and organoheterotrophs (Bathyarchaeia) in deep sediments. Among the 37 MAGs, Gammaproteobacteria, Desulfobacteriota, and Methylomirabilota were the most common in the microbial community. Metagenome sequencing revealed the assembled genomes genes for N, S, and CH₄ metabolism for carbon fixation, and genes encoding Fe and Mn pathways, indicating the likely coexistence of the biogeochemical cycle of various elements and creating certain conditions for the development of taxonomically and functionally diverse microbial communities.

Under laboratory conditions, the microbial communities of bottom sediments of a mud volcano Peschanka (Lake Baikal) were found to carry out anaerobic methane oxidation (AOM). After 16 days of...