The thesis is devoted to the study of regularities of reduction of chromium compounds by chrome-resistant sulfate-reducing bacteria. Microbiological investigations of waste waters of the city Lviv were carried out. Quantitative analysis of chromium-resistant microorganisms is shown among different groups. The concentration of hexavalent chromium was determined in waste waters during their purification. Dependences of distribution of chrome-resistant microorganisms of various groups were determined at different stages of waste waters purification. The most Cr (VI)-resistant microorganisms were determined. According to resistance to Cr (VI) microorganisms can be arranged in the following decreasing order: sulfate-reducing bacteria, cellulose-degrading microorganisms, yeast, nitrifying bacteria, nitrogen fixers, actinomycetes. Pure cultures of sulfate-reducing bacteria were isolated from sewage, which are able to detoxify water environment from Cr (VI). Isolated bacteria are obligate anaerobes, mesophiles. Optimal growth and hydrogen sulfide formation are observed under the temperature range 27-35°C and pH 7.0. Bacteria do not require vitamins of group B. Various organic compounds serve as electron donors for sulfate-reducing bacteria, cultivated in the medium with addition of sulfate. The best growth of isolated cultures is observed in the medium with lactate. Malate, glucose, fumarate, pyruvate, succinate, citrate, ethanol and fructose provided much smaller increase of biomass. Acetate, propionate, glycerol and butanol are not used by investigated bacteria. As a final electron acceptor bacteria effectively use sulfate, which results in its next reduction to hydrogen sulfide. Although under the absence of sulfate bacteria grow in the medium where the sole electron acceptor is Cr (VI), Fe (III), nitrate, fumarate or elemental sulfur. The studied sulfate-reducing bacteria, based on their morphological and physiological characteristics, belong to Desulfomicrobium genus according to Bergy determinant. It has been shown that addition of 5 mM of nitrate, 5 mM of sulfate and 0.5 mM of bichromate in the growth medium caused optimal conditions for bacterial growth. It has been shown that under the presence of сhromate and sulfate in the medium, CrO42? was used first. Herewith utilization of sulfate was inhibited. The inhibitory effect of chromate on sulfate reduction depends on chromate concentration in the medium. It was determined that sulfate reduction and hydrogen sulfide formation in the presence of chromate began after complete usage of CrO42? . The addition of nitrate and chromate into the medium caused inhibition of Desulfomicrobium sp. CrR3 growth and nitrate reduction in comparison with the growth and nitrate usage in the medium that contain nitrate only. Sulfate-reducing bacteria Desulfomicrobium sp. CrR3 are able to detoxify Cr (VI) at concentrations of 0.25-1 mM under the presence of various organic compounds in the growth medium. It is shown that biomass accumulation by bacteria Desulfomicrobium sp. CrR3 depends on concentration of heavy metal and presence of certain organic substances in the medium. Sulfate-reducing bacteria Desulfomicrobium sp. CrR3 are able to use fumarate as electron donor and acceptor. When they use fumarate as an electron acceptor succinate accumulates in the medium. If fumarate serves as electron donor, insignificant amounts of citrate, isocitrate and acetate are determined in addition to succinate. Under the simultaneous addition of fumarate, SO42- and CrO42- into the growth medium, the last inhibits usage of fumarate and SO42-. Key words: Microbe cenosis, Chrome-Resistant Sulfate-Reducing bacteria, Cr (VI) reduction, Purification of water environment.
