The Mechanism of Regulation of Chemolithotrophic Sulfur Oxidation in Pseudaminobacter salicylatoxidans KCT001

Abstract

Although the mode of repression of the sulfur oxidation (sox) operon has been elucidated in recent times the mechanism of its derepression is not yet known. Here we propose a comprehensive mechanism of sox gene expression by envisaging redox modulation of soxR as the key to the repression as well as derepression of sox-mediated thiosulfate oxidation Pseudaminobacter salicylatoxidans KCT001. While soxR, rendered to its reduced state by the action of soxS, keeps the sox system repressed, the oxidized species of the same protein is responsible for switching the system on. When thiosulfate appears in the medium, the basal amount of catalytic sox gene products, always present in the cells, convert 5–10% of supplied thiosulfate to sulfate without the participation of newly synthesized sox proteins. Sulfate produced from this basal level oxidation of thiosulfate can render the oxidation of soxR and thereby get converted to thiosulfate. This may be re-exported to the periplasm by the transmembrane protein soxT. This short cycle of conversion of thiosulfate to sulfate thus induces the expression of the sox genes.