Intracellular generation of superoxide by copper sulphate in Escherichia coli

Oxidative stress exerted by superoxide-generating agents such as paraquat triggers induction of the soxRS regulon of E. coli. In the system, SoxR protein is the superoxide-sensitive activator of the soxS gene. We found that copper sulphate (CuSO4) is a powerful inducer of soxS in a manner tightly dependent on both a functional soxR gene and the presence of molecular oxygen. E. coli strain lacking either superoxide dismutases or oxidative DNA repair enzymes was hypersensitive to killing by CuSO4. These results suggest that superoxide may be generated intracellularly by CuSO4 treatment, and that the generation may be involved in the Cu cytotoxicity.