Fractionation of sulfur isotopes during dissimilatory reduction of sulfate by a thermophilic gram-negative bacterium at 60 degrees C

Sulfur isotope ((34)S/(32)S) fractionation during reduction of dissolved sulfate was investigated with a growing batch culture of a thermophilic, gram-negative, sulfate-reducing bacterium (strain MT-96) at 60 degrees C. The completely oxidizing strain was isolated from geothermally heated sediments of a shallow-water hydrothermal vent in the Mediterranean Sea. The hydrogen sulfide produced in the experiments was enriched in (32)S by approximately 19 per thousand as compared to sulfate, which indicates that stable isotope discrimination by this thermophile is within the range found previously for mesophilic sulfate-reducing bacteria, and only slightly higher than that observed for the thermophilic gram-positive Desulfotomaculum nigrificans.