Oxidation Systems of Sulfite and Thiosulfate

On the basis of the results mentioned above, S. novella seems to have the oxidation pathway of sulfur compounds as shown in Fig. 4.5, though another pathway may also occur. 

In Paracoccus vertusus, thiosulfate is oxidized directly to sulfate by the catalysis of an enzyme complex containing several cytochromes c but not cytochrome b (Kelly, 1989). Although sulfite-cytochrome c oxidoreductase occurs in the enzyme complex, the enzyme is thought not to participate in the oxidation of thiosulfate, because the rhodanese activity is not observed with the complex. However, as already indicated, it could be that as the enzyme complex contains a thiosulfatecleaving enzyme strongly bound to both the sulfur-accepting protein and sulfite-cytochrome c oxidoreductase, thiosulfate appears to be oxidized directly to sulfate. 

the thiosulfate-cleaving enzyme does not show rhodanese activity in the presence of the sulfur-accepting protein (Fukumori et al., 1989). 

Thiosulfate is found to be oxidized to tetrathionate by the catalysis of thiosulfate-cytochrome c oxidoreductase in Acidithiobacillus thiooxidans JCM 7814 (Nakamura et al., 2001), Thiobacillus tepidarius (Lu and Kelly, 1988a) and Thio-bacillus neapolitanus (Trudinger, 1961b). Tetrathionate is thought to be oxidized in the cytoplasm. But its oxidation mechanism has not been clarified. 

2 Sulfur-Oxidizing Bacteria Support Animals in the Dark on the Deep-Sea Bottom 

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