Anaerobic oxidation of petroleum hydrocarbons in enrichment cultures from sediments of the Gorevoy Utes natural oil seep under methanogenic and sulfate-reducing conditions.

This article presents the first experimental data on the ability of microbial communities from sediments of the Gorevoy Utes natural oil seep to degrade petroleum hydrocarbons under anaerobic conditions. Like in marine ecosystems associated with oil discharge, available electron acceptors, in particular sulfate ions, affect the composition of the microbial community and the degree of hydrocarbon conversion. The cultivation of the surface sediments under sulfate-reducing conditions led to the formation of a more diverse bacterial community and greater loss of n-alkanes (28%) in comparison to methanogenic conditions (6%). Microbial communities of both surface and deep sediments are more oriented to degrade polycyclic aromatic hydrocarbons (PAHs), to which the degree of the PAH conversion testifies (up to 46%) irrespective of the present electron acceptors. Microorganisms with the uncultured closest homologues from thermal habitats, sediments of mud volcanoes, and environments contaminated with hydrocarbons mainly represented microbial communities of enrichment cultures. The members of the phyla Firmicutes, Chloroflexi, and Caldiserica (OP5), as well as the class Deltaproteobacteria and Methanomicrobia, were mostly found in enrichment cultures. The influence of gas-saturated fluids may be responsible for the presence in the bacterial 16S rRNA gene libraries of the sequences of "rare taxa": Planctomycetes, Ca. Atribacteria (OP9), Ca. Armatimonadetes (OP10), Ca. Latescibacteria (WS3), Ca. division (AC1), Ca. division (OP11), and Ca. Parcubacteria (OD1), which can be involved in hydrocarbon oxidation.

[Microbial communities of the discharge zone of oil- and gas-bearing fluids in low-mineral 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. The sediments saturated with oil and methane were found to contain members of 10 bacterial and 2 archaeal phyla. The oxidized sediment layer contained methanotrophic bacteria belonging to the Alphaproteobacteria, which had a specific structure of the pmoA gene and clustered together with uncultured methanotrophs from cold ecosystems. The upper sediment layer contained also oil-oxidizing bacteria and the alkB genes most colsely related to those of Rhodococcus. The microbial community of reduced sediments exhibited lower diversity and was represented mostly by the organisms involved in hydrocarbon biodegradation.