Influence of the Escherichia coli oxyR gene function on λ prophage maintenance

In Escherichia coli hosts, hydrogen peroxide is one of the factors that may cause induction of λ prophage. Here, we demonstrate that H(2)O(2)-mediated λ prophage induction is significantly enhanced in the oxyR mutant host. The mRNA levels for cI gene expression were increased in a λ lysogen in the presence of H(2)O(2). On the other hand, stimulation of the p (M) promoter by cI857 overproduced from a multicopy plasmid was decreased in the ΔoxyR mutant in the presence of H(2)O(2) but not under normal growth conditions. The purified OxyR protein did bind specifically to the p (M) promoter region. This binding impaired efficiency of interaction of the cI protein with the OR3 site, while stimulating such a binding to OR2 and OR1 sites, in the regulatory region of the p (M) promoter. We propose that changes in cI gene expression, perhaps in combination with moderately induced SOS response, may be responsible for enhanced λ prophage induction by hydrogen peroxide in the oxyR mutant. Therefore, OxyR seems to be a factor stimulating λ prophage maintenance under conditions of oxidative stress. This proposal is discussed in the light of efficiency of induction of lambdoid prophages bearing genes coding for Shiga toxins.