How the RegBA Redox Responding System Controls Iron and Sulfur Oxidation in <i>Acidithiobacillus ferrooxidans</i>

Abstract

Valuable metals as well as ferrous iron and sulfur compounds are released from ore by ferric iron and sulfuric acid chemical attack. Biomining microorganisms allow the recycling of these products by oxidizing ferrous iron and/or sulfur compounds. The energy released from the oxidation of these substrates is used for the growth of the acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans. The respiratory pathways involved in these respiratory processes have been deciphered and the expression of the genes encoding these redox proteins is dependent on the electron donor present in the medium. Furthermore, in the presence of both ferrous iron and sulfur, the genes involved in iron oxidation are expressed before those involved in sulfur oxidation. We propose that the global redox responding two component system RegBA is responsible for this regulation since (i) the redox potential increases during iron oxidation but remains stable during sulfur oxidation and (ii) the transcriptional regulator RegA binds the regulatory region of a number of genes/operons involved in iron and sulfur oxidation. To understand the mechanism of the At. ferrooxidans RegBA system, the regA gene and the DNA corresponding to the DNA binding domain of RegA were cloned in an expression plasmid in Escherichia coli. The recombinant proteins, RegA and RegA-HTH respectively, were purified. The binding of RegA-HTH, phosphorylated and unphosphorylated RegA on the regulatory region of some target operons have been compared by gel shift mobility assay.