OXIDATION-STATE OF SULFUR IN THIOSULFATE AND IMPLICATIONS FOR ANAEROBIC ENERGY-METABOLISM

Disproportionation of thiosulfate is an important pathway in bacterial energy metabolism in anoxic sediments. It has been described as an in organic fermentation process in which a part of the molecule is oxidiz ed to sulfate, while the other stoichiometrically equivalent part is u sed as electron acceptor and reduced to sulfide. However, an intramole cular redox change is difficult to envisage because, according to the currently held view, the two sulfur atoms of thiosulfate exist in the oxidation state of sulfate (+6) and sulfide (-2) and do not change the ir respective oxidation states upon disproportionation. Our results ba sed on XANES spectroscopy indicate that the two different sulfur atoms in thiosulfate have charge densities corresponding to +5 and -1 oxida tion states which support a redox mechanism in the disproportionation of thiosulfate to sulfate and sulfide.