Role of RpoS regulon in resistance to oxidative stress and near-UV radiation in Delta oxyR suppressor mutants of Escherichia coli

Escherichia coli Delta oxyR mutants are hyper-sensitive to oxidative agents but this sensitivity is reversed to hyper-resistance in Delta oxyR suppressor strains (Delta oxyR(sup); Greenberg, J.T. and Demple, B. 1988. EMBO J. 7:2611-2618). Also, Delta oxyR mutants have increased mutation rates that are also reversed in Delta oxyR(sup). We now report that the rpoS regulon may have a role in determining hyper-resistance and loss of hyper-mutability of Delta oxyR(sup). Delta oxyR(sup) cells were also resistant to near-ultraviolet radiation (near-UV) and survived longer in stationary phase than Delta oxyR cells. In Delta oxyR(sup) cells elevated beta-galactosidase expression from a rpoS::lacZ promoter fusion and significant overproduction of RpoS protein was observed. These increases were accompanied by substantial elevation in transcription of rpoS-dependent genes as determined by beta-galactosidase expression from katE::lacZ, dps::lacZ, and xthA::lacZ promoters. Catalase HPI and HPII activities were also increased. When rpoS::Tn10 was transduced into Delta oxyR(sup), phenotypes switched back to hyper-sensitive, hyper-mutable and reduced catalases I and II. Individual Delta oxyR colonies exhibited significant clonal variability in beta-galactosidase expression from rpoS::lacZ promoter. These results provide further evidence of the functional and regulatory overlap between two major anti-oxidant defense systems of bacteria. (C) 1997 Elsevier Science Inc.