The Regulation of Sulfur Use By Ferrous Ion in Thiobacillus ferrooxidans

The use of elemental sulfur (S°) as an energy source by T. ferrooxidans AP19-3 was completely inhibited by above 108mM of Fe²⁺ added to S° (l %)-salts medium, in which about 0.6mM Fe²⁺ remained after 30 days cultivation without being oxidized. In contrast, the use of Fe²⁺ by this strain was not inhibited by S°. It was found that specific activities of hydrogen sulfide: ferric ion oxidoreductase (SFORase) and sulfite : ferric ion oxidoreductase, which are crucial in sulfur and sulfite oxidations of this strain, were completely inhibited by 20 mmand 1 mM Fe²⁺, suggesting that this may be a main cause for the cells not using sulfur as an energy source. The SFORase activity of the cells incubated with S°-Fe²⁺-salts medium decreased to 39% of that in control cells without Fe²⁺, suggesting that Fe²⁺ added to the medium inhibits a sulfite : ferric ion oxidoreductase, and as a results sulfite ions are accumulated in the cells and this damages the SFORase. Sodium sulfite completely inhibited cell growth on S°-salts medium at 0.1 mM, but not on iron-salts medium.