Phylogenetic diversity and activity of anaerobic microorganisms of high-temperature horizons of the Dagang oil field (P.R. China)

The number of microorganisms of major metabolic groups and the rates of sulfate reduction and methanogenesis processes in the formation waters of the high-temperature horizons of Dagang oil field have been determined. Using cultural methods, it was shown that the microbial community contained aerobic bacteria oxidizing crude oil, anaerobic fermentative bacteria, sulfate-reducing bacteria, and methanogens. Using cultural methods, the possibility of methane production from a mixture of hydrogen and carbon dioxide (H-2 + CO2) and from acetate was established, and this result was confirmed by radioisotope methods involving (NaHCO3)-C-14 and (CH3COONa)-C-14. Analysis of enrichment cultures 16S rDNA of methanogens demonstrated that these micro-organisms belong to Methanothermobacter sp. (M. thermautotrophicus), which consumes hydrogen and carbon dioxide as basic substrates. The genes of acetate-utilizing bacteria were not revealed. Phylotypes of the representatives of Thermococcus spp. were found among archaeal 16S rDNA. 16S rRNA genes of bacterial clones belong to the orders Thermoanaerobacteriales (Thermoanoerobacter, Thermovenabulum, Thermacetogenium, and Coprothermobacter spp.), Thermotogales, Nitrospirales (Thennodesulfovibrio sp.) and Planctomycetales. 16S rDNA of a bacterium capable of oxidizing acetate in the course of syntrophic growth with H-2-utilizing-methanogens was found in high-temperature petroleum reservoirs for the first time. These results provide further insight into the composition of microbial communities of high-temperature petroleum reservoirs, indicating that syntrophic processes play an important part in acetate degradation accompanied by methane production.