FOR MOTION OF COPPER SULFIDES BY DESULFOVIBRIO SP. R2UNDER OPTIMAL TEMPERATURE CONDITIONS

Sulfate-reducing bacteria play an important role in metal sulfide formation in anaerobicenvironments as well as various technological schemes. The major mechanism ofmetal precipitation by SRB is formation of insoluble sulfides. The study of metal sulfideformation, including copper, by pure cultures of SRB is hampered by metal ions toxicityto the bacteria. The copper-tolerant Desulfovibrio have been recently isolated and described(Karnachuk et al., 2003; Karnachuk et al., 2008). This study focuses on revealingthe optimum temperature range for growth and sulfide production by copper-tolerantDesulfovibro sp., R2 and examination of copper sulfides formed by the bacteria underthe optimum temperature conditions.Specific growth rate (μ), lag-phase and doubling time (Td) have been determined forDesulfovibrio sp. R2 growing in the batch culture with lactate as electron donor at thetemperature range of +18 to +38°C. The maximum μ of 0,37± 0,15 h-1, minimum lagphaseof 4 h, and doubling time of 2.12 h was observed under +35°C. The maximum sulfideconcentration did not change substantially at the studied temperature range, and themaximum biomass production was detected at +28°C. This temperature has been chosento study copper sulfide production because cell surface plays major role in initial metalbinding. Cell wall also may be a nucleation site for the subsequent formation of crystallinemetal sulfides.Precipitates formed in Desulfovibrio sp. R2 spent cultures have been studied byscanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Shortterm(9 days) incubation experiments resulted in production of smaller particles with theaverage size 75 μm whereas particles up to 300 μm were formed during long-term (58days) incubations. Cu and S were major peaks revealed by EDS analysis. Cu also had anintense EDS signal in the control abiogenic precipitate obtained without SRB inoculum.On the other hand, abiogenic control showed only minor S peak. Cu:S ratio in biogenicprecipitate was consistent with mineral covellite (CuS) under the long-term incubation.Minor peaks of Fe, P, and O occurred in both, experiment and control. These elementsmay be ascribed to the copper oxide and iron-copper-phosphates. The formation ofmixed copper-iron sulfides is also possible under the biogenic incubation conditions.

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