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

When Thiobacillus ferrooxidans API9-3 that had been treated to remove iron from the cell surface was incubated aerobically with both elemental sulfur and o-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+ wasprobably produced as an intermediate during the oxidation of elemental sulfur.Sulfur-grown cells that were cultured successively in a sulfur-salt mediumalways had high levels of iron-oxidizing activity.The strain could use Fe2+ produced earlier by the FIR system for growth.Weconcluded that when T. ferrooxidans API9-3 grows on a sulfur-salt mediumunder aerobic conditions, the strain used a sulfur oxidation route not reported before that comprises both the FIR and iron-oxidizing systems.Thiobacillus ferrooxidans uses both ferrous ions and the sulfur moiety in sulfide ores for growth.This makes the organism valuable for bacterial leaching of sulfide ores.Many in-