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

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