Selective inhibition of the oxidation of ferrous iron or sulfur in Thiobacillus ferrooxidans

Abstract

The oxidation of either ferrous iron or sulfur by Thiobacillus ferrooxidans was selectively inhibited or controlled by various anions, inhibitors, and osmotic pressure. Iron oxidation was more sensitive than sulfur oxidation to inhibition by chloride, phosphate, and nitrate at low concentrations (below 0.1 M) and also to inhibition by azide and cyanide. Sulfur oxidation was more sensitive than iron oxidation to the inhibitory effect of high osmotic pressure. These differences were evident not only between iron oxidation by iron-grown cells and sulfur oxidation by sulfur-grown cells but also between the iron and sulfur oxidation activities of the same iron-grown cells. Growth experiments with ferrous iron or sulfur as an oxidizable substrate confirmed the higher sensitivity of iron oxidation to inhibition by phosphate, chloride, azide, and cyanide. Sulfur oxidation was actually stimulated by 50 mM phosphate or chloride. Leaching of Fe and Zn from pyrite (FeS(2)) and sphalerite (ZnS) by T. ferrooxidans was differentially affected by phosphate and chloride, which inhibited the solubilization of Fe without significantly affecting the solubilization of Zn.

FIG. 1

Effects of concentrations of various anions, sucrose, and β-alanine on the oxidation of ferrous iron and sulfur in iron-grown T. ferrooxidans strain SM-4 and of sulfur in sulfur-grown T. ferrooxidans strain SM-4. Please note the different scales on the y axes.

FIG. 2

Effect of phosphate concentration on oxygen consumption. (A) Growth of T. ferrooxidans on Fe²⁺; (B) growth of T. thiooxidans on S⁰.

FIG. 3

Effect of phosphate concentration on carbon dioxide consumption. (A) Growth of T. ferrooxidans on Fe²⁺; (B) growth of T. thiooxidans on S⁰.

FIG. 4

Effect of phosphate concentration on the extraction of Fe and Zn from a mixture of pyrite and sphalerite.