Bacterial Reduction of Tetrathionate

Abstract

THE power of reducing nitrate is widespread among micro-organisms, while the reduction of sulphate is restricted to a few species¹. It has long been recognized, however, that many bacteria are able to reduce less highly oxidized inorganic sulphur compounds (tetrathionate, thiosulphate, sulphite, etc.) to hydrogen sulphide². In the course of attempts to improve selective media for isolating Salmonellas and Bact. typhosum from excreta, we have found that, so far as some organisms are concerned, the tetrathionate is first reduced to thiosulphate. This reaction takes place rapidly and quantitatively, and estimations at different stages show that the molecular concentration of the thiosulphate formed is twice that of the tetrathionate which has disappeared, in agreement with the equation: The subsequent further reduction of thiosulphate to hydrogen sulphide is, in comparison, so slow that the reduction of tetrathionate can be followed accurately by direct iodometric titration of the thiosulphate, provided that the high acidity developing from accumulat on of thiosulphuric acid is controlled by a phosphate buffer.