Studies on thiobacillus denitrificans

Summary Experiments with T. denitrificans have shown that this bacterium cannot develop in media devoid of ammonium salts, and that iron is required for growth. Pure cultures have been isolated by means of a modified medium which permits rapid growth in serial transfers. The organism has been characterized as an obligatory chemoautotroph which can oxidize a number of inorganic sulfur compounds (elementary sulfur, thiosulfate, tetrathionate) either aerobically with O₂, or anaerobically with nitrate as oxidant.Nitrite was found to be highly toxic to the nitrate-reducing enzyme system; concentrations as low as 3.5 · 10^-4 m inhibit denitrification in the presence of sulfur about 40%. In the presence of thiosulfate, nitrite is rapidly decomposed to NO; this gas can subsequently be used as an oxidant, and is reduced to N₂. The formation of NO depends on the presence of both thiosulfate and nitrite.With resting cell suspensions CO₂ assimilation has been established; the assimilation products are not merely carboxylation products, as demonstrated in experiments with C¹⁴O₂.