Thiosulfate reductase as a chlorate reductase inSalmonella typhimurium

The contribution of thiosulfate reductase to chlorate sensitivity in Salmonella typhimurium was examined. Electrophoresed extracts of nitrate-grown cells of both the wild type and a chlC mutant were shown to contain chlorate reductase activity of the same relative mobility as a thiosulfate reductase activity which was present in the chlC mutant, but not in the wild-type grown under these conditions. A mutation is phs, which is essential for thiosulfate reductase by S. typhimurium, was shown to confer some chlorate resistance in the wild-type background and to increase the chlorate resistance obtained with a chlC mutation. Finally, thiosulfate in the anaerobic growth medium was shown to protect a chlC mutant growing in the presence of chlorate, but it did not protect the wild type. The results are consistent with a picture in which thiosulfate reductase can function as a chlorate reductase in both the wild-type and chlC backgrounds, although its capacity to reduce thiosulfate is diminished by the presence of an active nitrate reductase encoded by chlC.