New approaches to assessing the transformation of soil microbial communities in the soil surface horizons of Rostov-on-Don

The aim of this work was to study the activity and composition of soil microbial communities, their resistance to heavy metals and polycyclic aromatic hydrocarbons to develop approaches for assessing the transformation of microbial communities in Urbic Technosol. To determine the physicochemical properties and analyze microbiological indicators, soil sampling was carried out in the city of Rostov-on-Don – a large industrial city located in the steppe zone. Anthropogenically transformed soils and zonal soil – natural soils samples were collected. In anthropogenically transformed soils, a slight excess of the approximately permissible concentration of Zn (up to 244 mg/kg) and a significant excess of the maximum permissible concentration of benzo[a]pyrene (up to 400 ng/g) were found. The most sensitive indicators of urbanization were the number of streptomycetes and nitrification activity, which were 2–4 times lower in the urban soils. Despite the absence of changes in the number of other ecotrophic groups of microorganisms, such as copiotrophs, prototrophs, amylolytics, proteolytics, denitrifiers, a change in community composition was observed in anthropogenically transformed soils, with an increase in the proportion of pigmented microorganisms. Among them, actinobacteria capable of PAH degradation (Kocuria, Gordonia and Rhodococcus), as well as those tolerant to Cd, were identified. Thus, under the influence of urbanization, a restructuring of microbial communities occurs, which makes it possible to propose new bioindicators for the assessment of urban soils.