The oxidation of thiosulfate and phosphorylation in extracts of Thiobacillus thioparus.

Thiobmillus thioparus is an autotrophic microorganism that obtains the energy required for growth by the oxidation of reduced inorganic sulfur compounds to sulfate. When it is grown on high concentrations of thiosulfate, the organism accumulates elemental sulfur and produces sulfate. The pathway of thiosulfate oxidation has been essentially unknown; however, it has been postulated that tetrathionate and other polythionates are intermediates in this oxidation (1). Recent evidence indicates that inorganic orthophosphate is involved in the oxidation of thiosulfate by this organism since the presence of inorganic orthophosphate or arsenate (2) is required for the complete oxidation of thiosulfate to sulfate. Santer (3) showed that during the oxidation of thiosulfate in the presence of 01*-labeled inorganic orthophosphate, 0’8 is transferred to the sulfate that is produced in the oxidation. The specific activity of the 018 found in the sulfate was approximately one-fourth of that found in the inorganic orthophosphate. Recently, Peck (4) postulated a reaction sequence for the oxidation of thiosulfate by T. thioparus that explains these observations (Equations 1 to 6).’