Lack of YggX results in chronic oxidative stress and uncovers subtle defects in Fe-S cluster metabolism in Salmonella enterica

As components involved in Fe-S cluster metabolism are described, the challenge becomes defining the integrated process that occurs in vivo based on the individual functions characterized in vitro. Strains lacking yggX have been used here to mimic chronic oxidative stress and uncover subtle defects in Fe-S cluster metabolism. We describe the in vivo similarities and differences between isc mutants, which have a known function in cluster assembly, and mutants disrupted in four additional loci, gshA, apbC, apbE, and rseC. The latter mutants share similarities with isc mutants: (i) a sensitivity to oxidative stress, (ii) a thiamine auxotrophy in the absence of the YggX protein, and (iii) decreased activities of Fe-S proteins, including aconitase, succinate dehydrogenase, and MiaB. However, they differ from isc mutants by displaying a phenotypic dependence on metals and a distinct defect in the SoxRS response to superoxides. Results presented herein support the proposed role of YggX in iron trafficking and protection against oxidative stress, describe additional phenotypes of ise mutants, and suggest a working model in which the ApbC, ApbE, and RseC proteins and glutathione participate in Fe-S cluster repair.