ИСТИНА

The Black Sea is a largest meromictic sea, where anaerobic, sulfide-rich deep waters do not mix with the upper, oxygenated water layer. Molecular biological analyses revealed sulfate-reducing bacteria (SRB) of Desulfotomaculum, Desulfovibrio, and Desulfobacter genera in both anaerobic and aerobic zones of the Black Sea. A pure culture of psychrophilic gram-negative asporogenous SRB, with 99% 16S rRNA gene homology to Desulfofrigus fragile, was isolated for the first time from sub-surface water layer. We analyzed the presence of the main antioxidative defence genes of SRB (superoxide dismutase, desulfoferrodoxin, rubrerythrin, rubredoxin:oxygen oxidoreductase, cytochrome bd ubiquinol oxidase, cytochrome c oxidase, bacterioferritin, alkyl hydroperoxide reductase, hybrid-cluster protein) in the Desulfofrigus sp. genome. In addition, it was shown that NADH significantly increased O2 reduction by whole cells of Desulfofrigus sp. The concentration of cytochrome c in cells was 0.44 nmoles/mg protein. We observed that Desulfofrigus sp. almost completely retained growth and sulfate-reducing activity at 1 mM O2 in the culture medium. DOP-PCR was used for detection of antioxidative defence genes. Oxygen reduction rates were measured by oxymetry with the Clark oxygen electrode. Sulfate reduction rates were measured by using a radioisotope 35S-SO4 and culture growth - by DAPI-stained cell counting under an epifluorescence microscope. We isolated a marine SRB that belongs to the Desulfofrigus genus and exhibits a high aerotolerance capability. We propose that this aerotolerance is linked to various oxygen and ROS detoxification systems found in the bacterium.