In the Republic of Kazakhstan (one of the top 10 oil-producing countries in the world), the remediation of oil pollution found in unproductive soils under the conditions of a sharply continental arid climate is a highly relevant problem. The aims of this work are to study the biodegradation capacity of the gray soil of the ‘Daulet Asia’ landfill, assess the degradative potential of indigenous oil-degrading strains and changes in the composition of the soil microbial community. Analytical chemistry methods, distillation and chromatographic mass spectrometry were used for oil analysis; gravimetry and IR spectroscopy were used to evaluate oil degradation. Standard microbiological techniques were employed to isolate and cultivate microorganisms and metagenomic sequencing was carried out using Oxford Nanopore technology. Raw data processing and subsequent analysis were performed using modern software packages. Three isolated strains of interest were identified based on the analysis of 16S rRNA gene fragment sequences. The studied soil has low biodegradation capacity (oil loss was 6.2% on day 60), possibly due to the low abundance and weak activity of indigenous hydrocarbon-oxidizing microorganisms. The taxonomic composition of the microbiome in the studied soil suggests some potential for oil degradation. Assessment of the effectiveness of oil degradation by the indigenous microbiome indicates that this potential can be realized only marginally in situ. Isolated oil-degrading strains were identified as belonging to the Rhodococcus and Kocuria genera. Effective oil removal from the studied soil requires the introduction of active microorganisms (e.g., as part of biopreparations). Considering the characteristics of the hot arid climate, for bioremediation of contaminated sierozems of Southern Kazakhstan, it is advisable to use halotolerant oil-degrading microorganisms with a wide temperature range that are capable of degrading hydrocarbons under moisture deficiency.

The self-purification capacity of oil-contaminated soils is largely determined by the metabolic activity of autochthonous oil-oxidizing microorganisms. This study examined three strains of actinobacteria, which are hydrocarbon degraders, isolated from oil-contaminated sierozem soil at the Daulet Asia landfill (Southern Kazakhstan). Functional gene analysis was conducted (genome completeness > 98%, and contamination < 3%), and the phenotypic properties of these bacterial strains were studied to assess their potential for bio- and phytoremediation technologies in the sharply continental arid climate of the Aral Sea region. The isolated strains Rhodococcus kroppenstedtii K18 and MF2 and Kocuria rosea K1 grow on oil (12–22% oil loss after 10 days of cultivation in liquid mineral salt medium) and diesel fuel and can utilize hexadecane and benzoate as the sole source of carbon and energy. Furthermore, Rhodococcus K18 and MF2 utilize dodecane and eicosane, while K. rosea K1 utilizes phenol and gentisate. A significant decrease in surface tension (to 31.4 mN/m) observed during cultivation of strains K18 and MF2 on minimal salt medium indicates the secretion of surfactants that increase the bioavailability of hydrophobic substrates. The studied strains possess a number of properties that promote plant growth: they produce auxins, solubilize calcium hydroxyapatite, and protect plants from infection by the phytopathogenic microorganisms Fusarium oxysporum and Pectobacterium wasabiae. Actinobacteria are compatible when co-cultivated, as no mutual growth inhibition was observed. This study expands our understanding of typical bacterial representatives of desert soil, and this may contribute to the development of bioremediation approaches for the restoration of disturbed biotopes under extreme environmental conditions.

The efficiency of bioremediating oil-contaminated serozem (gray desert soil) of Southern Kazakhstan was investigated in the study. The first stage involved choosing hydrocarbon-degrading microorganisms suitable for the bioremediation of this desert soil. The second stage assessed the bioremediation potential of the selected microorganisms in laboratory microcosms. The final stage was a field trial experiment investigating oil removal under conditions of in situ natural attenuation, biostimulation (application of NPK fertilizer Nitroammophoska), reintroduction of indigenous oil-degrading microorganisms isolated from soils of the Aral Sea region and bioaugmentation using degrader strains from the laboratory collection. Additionally, the resulting native desert soil microbiomes were compared. Results showed that natural attenuation of the desert soil occurred over two months (with 68.5% of hydrocarbons removed), while biostimulation, reintroduction, and bioaugmentation were—as expected—also effective, achieving 89.4–97.0% oil removal. In the contaminated soil during the spring season, a significant increase in the proportion of Gammaproteobacteria within the soil microbiome was observed, with Alphaproteobacteria and Bacilli also representing significant fractions.