Production of ferrous ions as intermediates during aerobic sulfur oxidation in Thiobacillus ferrooxidans.

Abstract

When Thiobacillus ferrooxidans AP19-3 that had been treated to remove iron from the cell surface was incubated aerobically with both elemental sulfur and 6>-phenanthroline, Fe3+ still present was reduced by the ferric-ion reducing (FIR) system of the cells. Ferrous ion chelated with o-phenanthroline was not be oxidized by iron oxidase, and leaked out into the reaction mixture. In the absence of o-phenanthroline, however, Fe2+ was not detected, suggesting that it was rapidly reoxidized by iron oxidase. Sulfur oxidation by this strain under aerobic conditions was strongly inhibited by o-phenanthroline, so Fe2+ was probably produced as an intermediate during the oxidation of elemental sulfur. Sulfur-grown cells that were cultured successively in a sulfur-salt medium always had high levels of iron-oxidizing activity. The strain could use Fe2+ produced earlier by the FIR system for growth. We concluded that when T. ferrooxidans AP19-3 grows on a sulfur-salt medium under aerobic conditions, the strain used a su...