A sulfate, sulfite and thiosulfate incorporating system in Candida utilis

Sulfate, sulfite and thiosulfate incorporation in the yeast Candida utilis is inhibited by extracellular sulfate, sulfite and thiosulfate and by sulfate analogues selenate, chromate and molybdate. The three processes are blocked if sulfate, sulfite, thiosulfate, cysteine and homocysteine are allowed to accumulate endogenously. Incorporation of the three inorganic sulfur oxy anions is inactivated by heat at the same rate. Mutants previously shown to be defective in sulfate incorporation are also affected in sulfite and thiosulfate uptake. Revertants of these mutants selected by plating in ethionine-supplemented minimal medium recovered the capacity to incorporate sulfate, sulfite and thiosulfate. These results taken together with previous evidence demonstrate the existence of a common sulfate, sulfite and thiosulfate incorporating system in this yeast.