Reduction of tetrazolium salts by sulfate-reducing bacteria

The reduction of tetrazolium salts by the sulfate-reducing bacteria, Desulfovibrio desulfuricans and Desulfotomaculum orientis, was examined. D. desulfuricans and D. orientis reduced triphenyltetrazolium chloride (TTC) and 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) forming intracellular formazan deposits. The reduction rate of INT was higher than that of TTC. INT reduction was not inhibited by the addition of sulfate or molybdate, and sulfate uptake was inhibited by the addition of both INT and molybdate. The ratio of intracellular formazan forming cells to acridine orange direct counts in both strains decreased with culture age and starvation time.