Defining the role of two sulfur dioxygenases of Azotobacter vinelandii in sulfur trafficking

Abstract

The human ETHE1 gene encodes sulfur dioxygenase (SD) which, together with likely participation of sulfurtransferase (rhodanese), is essential for sulfide detoxification in mitochondria. The current work describes a similar pathway in Azotobacter vinelandii. This Gram‐negative bacterium has two ETHE1‐like genes (Avin_46910 & Avin_01930) potentially involved in sulfide clearance. Biochemical and genetic approaches were used to test if these genes encode SD. The corresponding proteins (SD1 and SD2) were purified and had strong SD activity (sulfur‐ and glutathione‐dependent consumption of oxygen; ~25 U/mg). The SD1 gene is found in the same operon with genes for a SulP family transporter (sulP) and a rhodanese (rhdB). Glutathione persulfide, the substrate for SD, could be generated by RhdB using thiosulfate as sulfur donor and glutathione as sulfur acceptor, implying tight coupling of the rhodanese and SD reactions. Mutant strains deficient in SD1 and/or SD2 were constructed. Higher levels of sulfide accumulated in the double mutant compared to the wild type and single mutants during late log and stationary phase of growth with sulfate as sulfur source. During growth with thiosulfate, the double mutant achieved lower cell density and accumulated more sulfide relative to the wild‐type strain. The results indicate that these SDs participate in oxidation of sulfide. Supported by Fralin Life Sciences Institute.