OXIDATION OF THIOSULFATE TO TETRATHIONATE BY HETEROTROPHIC BACTERIA FROM AQUATIC ENVIRONMENTS

We have studied 11 strains of the most active heterotrophic bacteria oxidizing thiosulfate to tetrathionate. Most strains oxidize thiosulfate in parallel with the growth of the cultures on organic media, the system of thiosulfate oxidation being of a constitutive nature. The thiosulfate oxidizing activity in the strains studied varies within a range of one to two orders of magnitude, reaching 400 mumoles/mg protein.h in the most active marine pseudomonad strain from the Black Sea. This bacterium is also capable of reducing tetrathionate to thiosulfate in the presence of acetate. We observed in all strains inhibition of thiosulfate oxidation on addition of acetate to cell suspensions. We detected in cell-free extracts of all strains thiosulfate-ferricyanide- and thiosulfate-cytochrome-c-oxidoreductase activity. In the majority of strains addition of thiosulfate to cell-free extracts caused rapid reduction of endogenous cytochromes c, while addition of oxidized cytochrome C550 increased the activity of thiosulfate oxidation by cell-free extracts of all bacteria studied.