FEATURES OF BACTERIAL COMMUNITIES OF BOTTOM SEDIMENTS IN THE AREA OF CHRONIC HYDROCARBON ENTRY

Abstract

The Kamenka River flows through the territory of the Kokuy oil and gas field. A unique feature of this area is the
presence of karst processes in the underlying rocks. As a result, oil spreads in underground horizons over significant distances from
the oil extraction sites and emerges on the soil surface and in riverbeds at locations not associated with the operation of oil wells. The
prolonged presence of petroleum hydrocarbons in soils and bottom sediments leads to successional changes in the composition of
cenoses. Microbial communities respond the fastest, which is due to the ecological plasticity of bacteria. This study examines the
composition of bacterial communities in the bottom sediments of the Kamenka River. The analysis of microbiocenoses was performed
based on high-throughput sequencing data and classical microbiological methods, which allowed for the isolation of key ecologicaltrophic groups. Sampling was conducted at a site where petroleum hydrocarbons emerged into the riverbed, as well as upstream and
downstream. The concentration of oil in the collected samples ranged from 2.4 to 25.8 g/kg. It was found that the dominant phylotypes
in the studied communities were representatives of Proteobacteria (16.7–30.3%), among which the classes Alphaproteobacteria (3.2–
8.7%) and Gammaproteobacteria (13.4–21.5%) were identified. The microbial community at the site of oil hydrocarbons’ emergence
exhibited the highest phylogenetic diversity, according to the values of Shannon and Simpson indices. It has been established that there
exists a core group of microorganisms that forms the basis of the microbiocenoses in this study area and a variable group whose
composition depends on selective factors changing along the river's flow. In the microbial communities, the proportion of oil-degrading
microorganisms varied from 0.02% to 16.0% and was in direct correlation with the concentration of hydrocarbons in the bottom sediments. An analysis of the metabolic potential of cultivated microorganisms revealed the presence of aerobic bacteria capable of utilizing
aromatic compounds as a carbon source.