A novel type of energy metabolism involving fermentation of inorganic sulphur compounds.

Two processes are known whereby energy is conserved during substrate metabolism in heterotrophic organisms: respiration and fermentation. Both involve oxidation–reduction reactions; but whereas in respiration the electrons are transferred from substrate to an electron acceptor, in fermentation part of the substrate molecule itself accepts the electrons. Fermentation is therefore a type of disproportionation, and does not involve an overall change in oxidation state of the substrate. All fermentative substrates known to date are organic molecules. We have discovered a novel type of fermentation involving the disproportionation of inorganic sulphur compounds in certain sulphate-reducing bacteria1. Initially discovered in a newly isolated sulphate-reducing bacterium, Desulfovibrio sulfodismutans, the capacity for disproportionation of sulphur compounds is also found in some known sulphate-reducing bacteria and various bacteria isolated from freshwater, brackish or marine sediments.