Antibiotics in the soil and their effect on the soil microbiot

Antibiotics have been crucial in the fight against infectious diseases for the past 50 years. In agriculture they are widely used in the treatment of animals, birds and aquaculture, to prevent spoilage of feed, as stimulators of growth and productivity of livestock, in the production of essential amino acids as impurities in feed, and so on. At present, the use of antibiotics in animal husbandry has become excessive due to the prevention of global epidemics. In turn, the ingress of antibiotics into water and soil, in particular through organic fertilizers, poses a potential threat to these environments. Thus, a variety of antibiotic resistance genes (GRAs) are spreading in soil microorganisms, which is currently a global health problem. It is believed that the stability of antibiotics after entering the soil is mainly due to their rate of decomposition and sorption to the organic soil matrix. A wide range of values of the half-life (DT50) of these compounds in soils indicates that their stability depends on a number of factors: soil properties, climatic conditions (temperature, precipitation, and humidity), physicochemical characteristics of antibiotics. High antimicrobial activity of antibiotics in the soil differentially inhibits the development of soil microorganisms, affects their species composition, which can cause changes in the ecological functionality of the soil. Thus, even low concentrations of antibiotics significantly reduce soil respiration. This phenomenon is especially noticeable in the presence of sulfamethoxazole, sulfamethazine, sulfadiazine and trimethoprim in the soil. The presence of antibiotics in the soil affects the processes of nitrification and / or denitrification, and the inhibition of these processes depends on the duration of exposure and the type of compound. Monensin and chlortetracycline at concentrations of 0.01–0.1 and 0.0003–0.3 mg/kg of soil do not affect nitrification at all. Antibiotics also affect the rate of iron transformation in the soil. Thus, sulfadiazine and monensin block the reduction of iron (Fe (III)) in the soil from a few days to 50 days. It should be noted that the lack of standardized tests hinders research that would lead to generalized conclusions about the effects of antibiotics on biogeochemical cycles, in particular on iron circulation. An important indicator of the response to antibiotics in the soil is considered to be the change in the enzymatic activity of dehydrogenase, phosphatase and urease of soil microorganisms, which may be associated with growth inhibition or death of sensitive microorganisms. In addition, the presence of some antibiotics in the soil can cause over-population of fungal populations, which are generally less sensitive to antibiotics than bacteria. There is evidence that antibiotics alter the enzymatic activity of soil microorganisms, especially they affect the ability to metabolize carbon of various origins. In addition, antibiotics not only affect the total number of microbiota, but also the relative content of different groups (gram-negative and gram-positive bacteria, fungi) in microbial populations. The importance of GRA studies of soil microorganisms is that they have led to the discovery of new genes responsible for bacterial resistance to antibiotics.