In the course of this work, the total numbers of heterotrophic microorganisms and the numbers of microbes participating in the nitrogen cycle (ammonifying, denitrifying, nitrifying, and nitrogen-fixing ones) in urban and natural (background) soils of Kogalym were estimated. A relation between the results obtained and the geochemical indicators was revealed. Our microbiological analysis showed the predominance of nitrogen-fixing microorganisms in urban soils (5.0 × 10⁴– 2.0 × 10⁶ CFU/g of soil), which were, on average, 44 less than in natural soils. In the last ones, the average number of denitrifying microorganisms was 7.0 × 10⁴ CFU/g of soil, exceeding 1.3 times their number in urban soils. Based on the information obtained, the microbial contents in the soils of Kogalym were established as a series: nitrogen fixators > ammonifiers > heterotrophs > denitrifiers; in background samples: denitrifiers > ammonifiers > heterotrophs > nitrogen fixators. According to the data of ecological and geochemical analysis, an excess of the MPC of mobile forms of heavy metals, such as Cu, Ni, and Zn, was revealed in the Eastern Industrial Zone of the city. A significant inverse correlation was revealed between the number of denitrifying microorganisms in the Kogalym soil microbiocenoses and the content of mobile Ni and Cu forms, which points to a possible negative effect of these metals on the development of denitrifiers. The minimum number of ammonifying, denitrifying, and nitrogen-fixing microorganisms was found in the Eastern Industrial Zone, especially in the soil samples that were taken near the railway. On the whole, the absence of noticeable differences in the microorganisms’ content of the studied groups in urban and natural soils indicates a low level of soil pollution in Kogalym. The results obtained represent the basis for subsequent ecological monitoring of the soils in the city and adjacent oil-producing areas, forecasting the environmental consequences of anthropogenic activities on these territories.

В результате почвенно-экологических исследований на территории города Балаково Саратовской области в 2023 г. выявлены две локальные техногенные геохимические аномалии. Установлено высокое содержание технофильных элементов и основные элементы- загрязнители почв – цинк, свинец, медь и никель. По уровню обогащенности гетеротрофными микроорганизмами почвы характеризуются как очень богатые (> 1×107 КОЕ/г почвы), на двух участках в промышленной зоне и на двух в рекреационной зоне – как богатые (1×107 КОЕ/г почвы). Среднее количество культивируемых аэробных гетеротрофных микроорганизмов в урбаноземах в 2 раза, в индустриоземах – в 3 раза ниже, чем в природных почвах. По уровню обогащенности микромицетами городские почвы варьируют от очень обедненных (< 2×106 КОЕ/г почвы) до богатых (1–2×107 КОЕ/г почвы). Зоны максимальной техногенной трансформации почв характерны для промышленных районов и жилой малоэтажной застройки с низким уровнем благоустройства. The soil-ecological studies (2023) conducted in the city of Balakovo, Saratov oblast allowed to detect two local technogenic geochemical anomalies with a high content of technophilic elements and major pollutants of soils (zinc, lead, copper and nickel). In terms of heterotrophic microorganisms enrichment, soils are characterized as highly rich (> 1×107 CFU/g), while in two sites of the industrial zone and in two plots of the recreational area as rich (1×107 CFU/g). The average number of cultivated aerobic heterotrophic microorganisms in urban soils is 2 times and in industrial 3 times lower than in natural soils. By micromycetes presence, urban soils range from very poor (< 2×106 CFU/g) to rich (1–2×107 CFU/g). Zones of maximum technogenic soil transformation are typical of industrial areas and low-rise residential buildings with bad amenities of life.

In the course of this work, the total numbers of heterotrophic microorganisms and the numbers of microbes participating in the nitrogen cycle (ammonifying, denitrifying, nitrifying and nitrogen-fixing ones) in urban and natural (background) soils of Kogalym were estimated. A relation between the obtained results with geochemical indicators was revealed. Our microbiological analysis showed the predominance of nitrogen-fixing microorganisms in urban soils (5.0×104 – 2.0×106 CFU/g of soil), which were on average 44 less than in natural soils. In the last ones the average number of denitrifying microorganisms was 7.0×104 CFU/g of soil, exceeding 1.3 times their number in urban soils. Based on the information obtained, microbial contents in the soils of Kogalym were established as a row: nitrogen fixators > ammonifiers > heterotrophs > denitrifiers; in background samples: denitrifiers > ammonifiers > heterotrophs > nitrogen fixators. According to the data of ecological and geochemical analysis, an excess of the MPC of mobile forms of heavy metals, such as Cu, Ni and Zn, was revealed in the Eastern Industrial zone of the city. A significant inverse correlation was revealed between the number of denitrifying microorganisms in the Kogalym soil microbiocenoses and the content of mobile Ni and Cu forms, which points to a possible negative effect of these metals on the development of denitrifiers. The minimum number of ammonifying, denitrifying and nitrogen-fixing microorganisms was found in the Eastern Industrial zone, especially in the soil samples that were taken near the railway. On the whole, the absence of noticeable differences in the microorganisms` content of the studied groups in urban and natural soils indicates a low level of soil pollution in Kogalym. The obtained results represent the basis for subsequent ecological monitoring of the soils in the city and adjacent oil-producing areas, forecasting the environmental consequences of anthropogenic activities in these territories.

Oil and petroleum products are a significant source of environmental pollution, leading to the accumulation of hydrocarbons in the soil profile. They contaminate groundwater, disrupt natural soil biochemical processes, interact with mineral compounds – thereby reducing their bioavailability to plants – and cause the poisoning and death of living organisms. The study of hydrocarbon-oxidizing microorganisms is of considerable practical importance due to their ability to degrade hydrocarbons. Analyzing the adaptation mechanisms and stress resistance of degrading bacteria enables the prediction of bioremediation efficiency under various ecological scenarios. This work investigates the influence of temperature, NaCl concentration, and pH on the growth and biofilm formation intensity of hydrocarbon-oxidizing bacteria isolated from soils with high levels of oil contamination. The substrate specificity of the oil-degrading bacteria was also studied. The strains Paenibacillus polymyxa S31 and Citrobacter freundii K29 were the most tolerant to abiotic environmental factors. P. polymyxa S31 exhibited the broadest substrate specificity, as it was capable of degrading all tested substrates. Maximum biofilm production by all studied strains was observed at 28°C. For strains Bacillus circulans D18, Bacillus licheniformis M88, Bacillus muralis V16, Bacillus pumilus L27, and P. glucanolyticus F15, the maximum production occurred in an alkaline environment (at pH 9), while for strains C. freundii K29 and P. polymyxa S31, it was in a neutral environment (at pH 7).

The substrate spectrum of hydrocarbon-oxidizing bacteria isolated from the soils of the Saratov region was studied: the soils of Balakovo (chronic anthropogenic pollution) and agricultural soils of Novokrivovka village (single hydrocarbon pollution). It was found that the microorganisms isolated from the urban soils of Balakovo, being under constant anthropogenic influence, had a wider substrate spectrum. It was revealed that 4 microorganisms isolated from the urban soils of Balakovo: Acinetobacter lwoffii R44, Bacillus circulans E75, B. horikoshii P22, Ochrobactrum gallinifaecis I59, and also Paenibacillus polymyxa S31, isolated from the soil of Novokrivovka village, were capable of decomposing the largest amount of hydrocarbon substrates, including crude oil and individual hydrocarbons. 100% of bacterial strains isolated from the soils of Novokrivovka village and 75% of microorganisms isolated from the soils of Balakovo used crude oil as the only carbon source. The number of bacteria capable of using aromatic hydrocarbons for growth was 2–3 times higher among isolates from the soils of Balakovo. Native hydrocarbon-oxidizing bacteria with a wide substrate spectrum can be used to design a biological product aimed at carrying out restoration activities of contaminated soil ecosystems.

It has been established that urban soils of one of the major oil-and-gas producing regions of Russia, located in the Far North (Kogalym, Khanty-Mansiysk Autonomous Okrug – Yugra), serve as a source of oil-degrading bacteria. A quantitative assessment was made of the degradative and emulsifying activity of the bacteria Bacillus alcalophilus WS-3027B, B. funiculus LY-2403G, B. halodurans MH-3011N, B. niacini TC-8101S, B. psychrodurans LV-1106E, and Curtobacterium flaccumfaciens AE-0851V with respect to oil. The maximum degree of oil degradation over 14 days was observed in the bacteria B. niacini TC-8101S (39.8%) and B. halodurans MH-3011N (36.0%). The highest endogenous (E24 = 70.0 and 53.0%; E48 = 68.7 and 62.0%) and exogenous (E24 = 74.0 and 58.6%; E48 = 74.0 and 54.0%) emulsifying activity was detected in the bacteria B. alcalophilus WS-3027B and B. funiculus LY-2403G. Based on the observed abilities of these bacteria to degrade and emulsify oil, as well as their high adaptive properties to low temperature, increased salinity, and alkaline environment, the use of these bacteria is recommended for the bioremediation of contaminated soils under Far North conditions.