Bacterial communities in sediments of Lake Baikal from areas with oil and gas discharge

Diversity and abundance of bacterial communities were investigated in methane hydrate-and oil-bearing sediments with different composition of pore waters at 6 sites in Lake Baikal, Siberia, using massively parallel sequencing (the Roche 454 platform). Sequences of Proteobacteria (17-48%), Actinobacteria (19-44%) and Cyanobacteria (17-48%) dominated the communities at all sites. Phylogenetic analysis of cyanobacterial sequences showed a large contribution of planktonic species and presence of uncultured lineages, whose representatives were detected in sediment communities of freshwater lakes. The ratio of different classes of Proteobacteria varied considerably: the Epsilon- and Delta-classes were the least represented, while the Alpha-, Beta-and Gamma-classes were the most represented. Some samples also showed a significant contribution of Bacteroidetes (7-13%), Chloroflexi (13%), candidate division OP10 and unclassified sequences (up to 16%). Other taxa made up less than 1%. Bacterial communities included a large number of unique phylotypes, whereas only few conventional phylotypes were detected. The phylotypes dominating the communities belonged to several taxa with cosmopolitan distributions. Their closest homologues involved liquid and gaseous hydrocarbons from deep sediments in biological cycles. Bacterial communities in Lake Baikal possessed moderate bacterial richness compared with other lake ecosystems.