Sulphide oxidation linked to the reduction of nitrate and nitrite in Thiobacillus denitrificans

1. Whole cells of Thiobacillus denitrificans reduce nitrite to NO, N2O and N2 when sulphide is the electron donor. 2. Crude extracts catalyse the oxidation of sulphide, which may be coupled to either oxygen, nitrate or nitrite as terminal acceptors. 3. The initial product of sulphide oxidation is a membrane-bound polymeric sulphur compound which is probably a polysulphide. This step is inhibited by CO. 4. In the absence of either nitrate or nitrite, sulphide is oxidized to polysulphide and sulphite. When nitrate is present, sulphide is oxidized to sulphate with a concomitant reduction of nitrate to nitrite. Under anaerobic conditions and in the presence of nitrite, sulphide is oxidized to polysulphide only. 5. Sulphite is oxidized to either adenosine 5′-phosphosulphate in the soluble fraction (S144) or to sulphate by the membrane fraction (P144). 6. A scheme for the oxidation of sulphide is proposed.

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