Comparison of the oxidation of thiosulfate and elemental sulfur by two heterotrophic bacteria and Thiobacillus thiooxidans

The rate and magnitude of the oxidation of thiosulfate (S₂O₃⁻) and elemental sulfur (S°) to sulfate, by two heterotrophic soil bacteria and Thiobacillus thiooxidans was compared in liquid medium and soil. The two heterotrophic organisms, Isolate 2, which oxidized S₂O₃⁻and Isolate 5, which oxidized S°, produced measurable and significant amounts of SO₄⁻in liquid media and autoclaved soil. Optimum heterotrophic oxidation occurred in autoclaved soil when the inoculated organisms were provided with an organic source of carbon as glucose. Conversely, glucose inhibited oxidation by T. thiooxidans, most likely via a build up of pyruvate. Under optimum conditions in autoclaved soil the rate and magnitude of heterotrophic oxidation were similar.