Role of Ferrous Ions in Synthetic Cobaltous Sulfide Leaching of Thiobacillus ferrooxidans.

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.