Investigation of microbial taxonomic diversity and of the rates of microbial processes of production and decomposition of organic matter made it possible to establish considerable diversity and activity of the sulfur cycle microorganisms in the microbial community of Lake Beloe (pH 9.4, salinity 3.1 g/L) upper sediment layer. According to the results of pyrosequencing, of the 16S rRNA gene, bacteria involved in H2 formation and oxidation were numerically predominant and highly diverse. The Hydrogenophaga spp. dominating in the community are aerobic or facultatively anaerobic chemoorgano- and chemolithoautotrophs using hydrogen oxidation as the source of energy. They play an important role in the transitory zones of mixing of subterranean and surface water.