Composition of the Microbial Communities of Bituminous Constructions at Natural Oil Seeps at the Bottom of Lake Baikal

Microbial communities of two bituminous constructions at the bottom of Lake Baikal in the region of natural oil seeps at a depth of 900 m have been investigated. Construction 8 contained biodegraded hydrocarbons, and construction 3, through which oil seeped, contained material that experienced biodegradation to a lesser degree. The composition of the microbial communities was studied by means of pyrosequencing of 16S rRNA gene fragments. Most of the bacterial 16S rRNA gene sequences identified in both bituminous constructions were attributed to proteobacteria, along with which Actinobacteria, Acidobacteria, Bacteroidetes, and TM7 were revealed. About 40% of the bacterial sequences in bituminous construction 3 belonged to representatives of uncultured groups within the classes Alphaproteobacteria and Betaproteobacteria and the phylum Bacteroidetes. The 16S rRNA gene sequences of archaea belonged to aceticlastic and hydrogenotrophic methanogens of the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales. The 16S rRNA genes of various groups of bacteria carrying out aerobic biodegradation of aromatic compounds and n-alkanes were found; their compositions differed between the constructions. Neither known groups of denitrifying betaproteobacteria nor known groups of sulfate-reducing deltaproteobacteria capable of carrying out anaerobic degradation of n-alkanes were found, which agrees with the low content of nitrate and sulfate in the water. In the anaerobic zone of bituminous constructions, the processes of biodegradation of hydrocarbons are probably carried out in the absence of alternative electron acceptors by the syntrophic community, including deltaproteobacteria of the genus Syntrophus and methanogenic archaea.