ROLE OF INORGANIC PHOSPHATE IN THIOSULFATE METABOLISM BY THIOBACILLUS THIOPARUS

Abstract

T. thioparus can completely convert thiosulfate to sulfate in the presence of inorganic phosphate. In the absence of phosphate, when the cells are adequately buffered, the total O2 uptake is approximately 70% of the theoretical amount required to convert all of the thiosulfate to sulfate. Phosphate also controls the rate of thiosulfate oxidation and is acting catalytically. Arsenate can substitute for phosphate. In a phosphate-free reaction mixture at least one S compound, tetrathionate, can be shown to accumulate. Experiments with thiosulfate, either S35SO3 or SS35O3, indicate that both S atoms are partially converted to sulfate in a phosphate-free reaction mixture whereas the rest accumulates in the supernatant of the reaction mixture. The complete oxidation of tetrathionate is also dependent on inorganic phosphate. These data suggest that tetrathionate is an intermediate in thiosulfate oxidation and that inorganic phosphate is required for a subsequent oxidative step at substrate level.