Studies on the Metabolism of Thiobacillus thiocyanoxidans

SUMMARY: The investigation of the metabolism of thiocyanate by pure cultures of Thiobacillus thiocyanoxidans was complicated by the fact that thiocyanate serves both as source of energy and as source of carbon and nitrogen. It was, therefore, difficult to separate oxidation from carbon dioxide fixation. The equation which best represented the resultant of these two processes was:

2KCNS + 5H2O + 3O2 = K2SO4 + (NH4)2SO4 + CO2 + (CH2O).

Thiocyanate was first hydrolysed to cyanate and sulphide. Cyanate was further hydrolysed to carbon dioxide and ammonia and sulphide was oxidized to sulphate. The oxidation of sulphide approximated to the equation:Na2S + 2O2 = Na2SO4. Gas uptakes were lower than would be expected from this equation, although special precautions were taken to prevent loss of sulphide.

Thiosulphate was oxidized to sulphate according to the equation:

Na2S2O3 + H2O + 2O2 = Na2SO4 + H2SO4.

Fixation of carbon dioxide after the oxidation of thiosulphate was shown, but the efficiency of energy utilization appeared lower than during the oxidation of thiocyanate.

Thioacetamide and thioacetic acid were oxidized to sulphate but this was believed to be preceded by a chemical breakdown to sulphide. Sulphite, metabisulphite, dithionite, dithionate, tetrathionate, trithionate, thiourea and cysteine were tested; no evidence was obtained of their utilization.