INFLUENCE OF HEXAVALENT CHROMIUM ON HYDROGEN-SULFIDE FORMATION BY SULFATE-REDUCING BACTERIA

The resistance of pure cultures of Desulfotomaculum nigrificans B-1492 and Desulfobacterium sp. strain 63 to various Cr6+(K2Cr2O7) concentrations was studied. Mesophilic strain 63, isolated from the bottom sediments of the Black Sea and represented by mobile (2.2 - 4.4) x (0.6 - 0.9) mu m rods, is capable of using hydrogen, formate, lactate, fumarate, malate, ethanol, and pyruvate as electron donors, realizing their complete oxidation to CO2. The culture does not grow on acetate, higher fatty acids, aromatic compounds, sugars, amino acids, or alcohols, with the exception of ethanol. Strain 63 also differs from the known species of the genus Desulfobacterium in the optimal growth temperature and the NaCl content in the medium. The minimum inhibitory chromium concentration for strain B-1492 was 70 mg Cr6+/1 (1.4 mM), for strain 63, growing in the medium with lactate - 52.5 mg Cr6+/1 (1.01 mM), and for strain 63, growing in the medium with ethanol 35 mg Cr6+/1 (0.7 mM). Both strains were able to remove Cr6+ from the growth medium; the highest removal (93.4%) was realized by strain 63 growing on ethanol. Low concentrations of Cr6+ stimulated the sulfate reduction process in the cultures of strain 63 (200% of the control) and strain B-1492 (270% of the control).