Heavy contamination of soils by crude oil is omnipresent in areas of oil recovery and exploitation. Bioremediation by indigenous plants in cooperation with hydrocarbon degrading microorganisms is an economically and ecologically feasible means to reclaim contaminated soils. To study the effects of indigenous soil bacteria capable of utilizing oil hydrocarbons on biomass production of plants growing in oil-contaminated soils eight bacterial strains were isolated from contaminated soils in Kazakhstan and characterized for their abilities to degrade oil components. Four of them, identified as species of Gordonia and Rhodococcus turned out to be effective degraders. They produced a variety of organic acids from oil components, of which 59 were identified and 7 of them are hitherto unknown acidic oil metabolites. One of them, Rhodococcus erythropolis SBUG 2054, utilized more than 140 oil components. Inoculating barley seeds together with different combinations of these bacterial strains restored normal growth of the plants on contaminated soils, demonstrating the power of this approach for bioremediation. Furthermore, we suggest that the plant promoting effect of these bacteria is not only due to the elimination of toxic oil hydrocarbons but possibly also to the accumulation of a variety of organic acids which modulate the barley's rhizosphere environment.

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Oil and oil products adversely affect both the biodiversity of the microorganisms and the soil function. In oil-contaminated soils, unique bacterial communities develop that are adapted to pollution. In this work, the bacterial structure and diversity of the microbial community have been studied in samples of oil-contaminated soils in Kazakhstan deposits using the Illumina MiSeq sequencer. The results of the study showed that the representatives of the following bacterial phyla dominated in the selected soil samples: Proteobacteria, prevailing in oil-contaminated soils (up to 48%), Actinobacteria (up to 29.33%), Firmicutes (up to 25.74%), Bacteroidetes (up to 33.28 %). The representatives of Planctomycetes, Verrucomicrobia, Chloroflexi (0.76%-4.62%) phyla were found in smaller amounts. All the uncontaminated soils were dominated by Micrococcaceae, Flexibacteraceae, Sphingomonadaceae, Planococcaceae, Flavobacteriaceae families, contaminated ones – by Halomonadaceae, Flavobacteriaceae, Alteromonadaceae, Dietziaceae, Pseudomonadaceae, Bacillaceae, Xanthomonadaceae, Anaerolinaceae, Mycobacteriaceae and Peptococcaceae families. At the genus level, samples of uncontaminated and contaminated soils also demonstrated significant diversity. The dominant bacterial genera in the samples of the uncontaminated soil were Hymenobacter, Arthrobacter, Gillisia. In contaminated soils of three deposits the microorganisms of the Halomonas, Marinobacter, Pseudomonas (mostly in 2KO soil sample), Bellilinea and Mycobacterium (mostly Md sample) genera were spread more widely; and a very large population of the microorganisms of the Halomonas genus was found in the contaminated soil sample from the Atyrau region. A comparison of the taxonomic structure of microbial communities of oil-contaminated soils indicates that the composition of the microbial population changes depending on the degree of oil pollution. Samples of uncontaminated background soils were characterized by higher bacterial diversity than samples of contaminated soils. The microorganisms belonging to the dominant phyla were mostly associated with the decomposition of oil hydrocarbons. The characterization of the bacterial communities living in the contaminated soils and the assessment of their ability to decompose oil can potentially be a guide for bioremediation of contaminated soils.

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The ability of thermotolerant oil-oxidizing microorganisms to degrade oil at elevated concentrations of NaCl has been studied. It was shown that the studied strains were capable of oil degradation under these conditions, and the temperature factor affects its degree.