Rokitko P. Composition of bacteria from the ChNPP 10-km zone and their resistance to gama-radiation and other stressful factors

The dissertation is devoted to analysis of the ecological consequences of the accident on Chernobyl Nuclear Power Plant (ChNPP) for bacteria. It was shown that in 1995-1996 the total number of soil bacteria was lower on 1-3 levels and the quantity of their species was lower on 30-40 % in comparison with soils outside zone. Thus, after accident the decrease of microbial diversity has occurred in ChNPP 10-km zone. It was established that in the ChNPP 10-km zone gama-irradiation resistant bacteria (Methylobacterium extorquens, M. mesophilicum, Bacillus subtilis, B. cereus, some nocardio- and coryneforms) prevailed quantitatively. These bacteria were also resistant to other stressful factors such as UV radiation, dehydration and hydrogen peroxide. All investigated Methylobacterium strains were resistant to gama-, UV radiation, hydrogen peroxide and dehydration. Therefore it is possible to assert that the resistance to these agents is a specific feature of Methylobacterium genus. The analysis of survival dose curves testifies that they have active repair systems of radiation sublethal damages which defined their high radioresistance, and, probably, has allowed to survive in radioactive soils ChNPP. It was established that the level of radioresistance in strains of the same species (Methylobacterium extorquens, M. mesophilicum, Bacillus subtilis, B. cereus) does not depend on their natural habitation (ChNPP 10-km zone or ecosystems with natural radioactive background).