ИСТИНА

Background: The Black Sea is a landlocked large meromictic basin which contains low-salinity surface water of riverine origin overlying high-salinity deep water. It is well known that sulfatereducing bacteria (SRB) of the anoxic water column play a major role in sulfide production in the Black Sea. Later experiments proved that sulfate reduction also occurs in the oxic layer and oxic-anoxic interface (chemocline zone). However, none sulfate-reducing microorganism from the Black Sea upper water column was identified and isolated in pure culture up to date. Objectives: Active enrichment cultures of SRB were obtained from the oxic water (30 and 70 m) and chemocline zone (120 m) of the Black Sea. The structure of anaerobic SRB communities in the enrichment cultures was analyzed using fluorescent in situ hybridization (FISH). Methods: Widdel's medium with some organic and non-organic additives was used to obtain the enrichment cultures of marine SRB from corresponding depths. FISH, restriction analysis and 16S rRNA sequencing were used for identification of microorganisms. Conclusions: Active enrichment cultures of SRB from the Black Sea chemocline zone were obtained on standard Widdel's medium, but addition of bichromate was required for growth of SRB enrichment cultures from the oxic water. The structure of the SRB communities in enrichment cultures differed significantly from that observed in native water samples, since conventional enrichment cultures did not reproducein situ conditions, especially those of the aerobic marine environment. The Desulfosporosinus sp. was a predominant SRB in the enrichment culture from the depth of 70 m.