Bioremediation potential of native microorganisms of the southern chernozem

Abstract

In the course of the conducted studies, main groups of soil microorganisms in the southern chernozem were identified. The resistance of isolates to the action of oil in the concentration range of 15–25%, the possibility of using it as a carbon source, the ability of soil microbiota to biodegradate oil in contaminated soil and the resistance of bacteria to low temperatures, high NaCl concentrations, acid and alkali resistance were established. 15 genera (31 species) of heterotrophic bacteria were isolated from uncontaminated soil samples of the southern chernozem subtype. Our assessment of the abundance dynamics of microorganisms isolated from laboratory contaminated soils showed that as a result of oil exposure, there was a significant decrease in the numbers of microorganisms: by the 180th day of our experiment, 10 bacteria species belonging to 3 genera were isolated, namely: Bacillus, Micrococcus and Serratia. Among the isolated bacteria, resistance to the action of the pollutant at a concentration of 25% was established for B. coagulans, B. mojavensis, B. megaterium, M. luteus, as well as for the museum strain of B. pumilus CM. By cultivating the studied bacterial strains on a carbon-free medium M9 with 15 and 20% oil added, their ability to use petroleum hydrocarbons as the only carbon source was established; however, when the concentration increased to 25%, only M. luteus, B. mojavensis and B. pumilus KM retained this ability. The presence of hydrocarbon-oxidizing bacteria in soil samples contributed to the 42% decrease in the oil mass concentration in 180 days. The most significant decrease in the concentration of petroleum products occurred in the period from the 10th to the 30th day and amounted to 25%, which is probably due to the increase in the numbers of heterotrophic bacteria. The ability to grow at a temperature of +4°C was established for representatives of the genus Bacillus, including the museum strain of B. pumillus CM, 4 strains of bacilli remained viable in an acidic environment (pH 5), 7 strains of bacilli and M. luteus and S. plymuthica remained viable in an alkaline environment (pH 9). The studied bacterial strains were growing on a GRM-agar with a NaCl concentration of 7%, the ability to grow at a NaCl concentration of 15% was preserved only by the museum strain of B. pumillus KM. The obtained results open the prospects for the use of hydrocarbon-oxidizing bacteria with a high adaptive potential as potential oil destructors capable of biodegradation at low temperatures, in conditions of high salinity and in a wide range of pH of the medium.