ABSTRACT
The properties of a ferric ion-reducing system which catalyzes the reduction of ferric ion with elemental sulfur was investigated with a pure strain of Thiobacillus ferrooxidans. In anaerobic conditions, washed intact cells of the strain reduced 6 mol of Fe with 1 mol of elemental sulfur to give 6 mol of Fe, 1 mol of sulfate, and a small amount of sulfite. In aerobic conditions, the 6 mol of Fe produced was immediately reoxidized by the iron oxidase of the cell, with a consumption of 1.5 mol of oxygen. As a result, Fe production was never observed under aerobic conditions. However, in the presence of 5 mM cyanide, which completely inhibits the iron oxidase of the cell, an amount of Fe production comparable to that formed under anaerobic conditions was observed under aerobic conditions. The ferric ion-reducing system had a pH optimum between 2.0 and 3.8, and the activity was completely destroyed by 10 min of incubation at 60 degrees C. A short treatment of the strain with 0.5% phenol completely destroyed the ferric ion-reducing system of the cell. However, this treatment did not affect the iron oxidase of the cell. Since a concomitant complete loss of the activity of sulfur oxidation by molecular oxygen was observed in 0.5% phenol-treated cells, it was concluded that the ferric ion-reducing system plays an important role in the sulfur oxidation activity of this strain, and a new sulfur-oxidizing route is proposed for T. ferrooxidans.
ABSTRACT
Microbiological leaching of synthetic cobaltous sulfide (CoS) was investigated with a pure strain of Thiobacillus ferroxidans. The strain could not grow on CoS-salts medium in the absence of ferrous ions (Fe). However, in CoS-salts medium supplemented with 18 mM Fe, the strain utilized both Fe and the sulfur moiety in CoS for growth, resulting in an enhanced solubilization of Co. Cell growth on sulfur-salts medium was strongly inhibited by Co, and this inhibition was completely protected by Fe. Cobalt-resistant cells, obtained by subculturing the strain in medium supplemented with both Fe and Co, brought a marked decrease in the amount of Fe absolutely required for cell growth on CoS-salts medium. As one mechanism of protection by Fe, it is proposed that the strain utilizes one part of Fe externally added to CoS-salts medium to synthesize the cobalt-resistant system. Since a similar protective effect by Fe was also observed for cell inhibition by stannous, nickel, zinc, silver, and mercuric ions, a new role of Fe in bacterial leaching in T. ferrooxidans is proposed.
