Thiosulphate Oxidation by Thiobacillus Strain C

1. Thiobacillus strain C oxidized [35S]thiosulphate completely to sulphate. 2. During thiosulphate oxidation [35S]sulphate was formed more rapidly from (S. 35SO3)2than from (35S *SO3)2-. 35S disappeared less rapidly from thiosulphate with (35S SO3)2as substrate than with (S.35SO3)2-. 3. Thiosulphate labelled in both atoms was produced during (35S * SO3)2oxidation, but not during (S. 35SO3)2oxidation. 4. No 35S was precipitated as elementary sulphur either in the presence or absence of exogenous unlabelled sulphur. 5. During [35S]thiosulphate oxidation, appreciable quantities of [35S]trithionate accumulated and later disappeared. Other polythionates did not accumulate consistently. 6. [35S]Trithionate was formed initially at a greater rate from (S.35SO3)2than from (35S.S03)2-, but subsequently at a similar rate from each. 7. Trithionate formed from (S .35SO3)2was labelled only in the oxidized sulphur atoms, but that formed from (35S .SO3)2was labelled in both oxidized and reduced atoms. The proportion of 35S in the oxidized atoms increased as more trithionate accumulated. 8. The results eliminate some mechanisms of trithionate formation but are consistent both with a mechanism of thiosulphate oxidation based on an initial reductive cleavage of the molecule and with a mechanism in which thiosulphate undergoes an initial oxidative reaction.