Specific features of the response of soil microbiota components to petroleum contamination

Oil and petroleum products are among the most hazardous pollutants affecting all stages of technogenesis. They pose a particular threat to soil ecosystems, which play a crucial role in biogeochemical cycles and the maintenance of ecological balance. Understanding the transformations that occur in soil under the influence of varying oil concentrations, as well as the responses of soil microorganisms to such contamination, is essential for the accurate assessment of soil ecosystem conditions and for selecting effective remediation strategies under specific circumstances. The aim of this study was to investigate the response of different components of soil microbiota—namely, various physiological groups of bacteria and microscopic fungi—to oil pollution across a wide concentration range. Experimental research was conducted on soil samples artificially contaminated with oil at the following concentrations: 1, 5, 10, 50, 100, 200, 300, and 500 cm³/kg. The results revealed a significant linear increase in the number of microorganisms from various ecological and physiological groups within the 10–100 cm³/kg concentration range. However, a further rise in oil concentration led to a marked decrease in bacterial abundance, except for hydrocarbon-oxidizing bacteria, which remained relatively stable. At the highest contamination level (500 cm³/kg), the soil microbiota was nearly completely suppressed, with only spore-forming and hydrocarbon-oxidizing bacteria persisting, indicating their ability to withstand toxic stress. Unlike bacteria, microscopic fungi exhibited a sharp decline in colony-forming units (CFU) at moderate oil concentrations (10–100 cm³/kg). Nonetheless, their abundance remained relatively stable at higher oil concentrations, and at 500 cm³/kg, the number of fungal CFUs was nearly twice that of bacteria. This suggests the presence of adaptive mechanisms in certain fungal taxa that enable survival under severe oil contamination.