title: The regulation and role of the periplasmic copper, zinc superoxide dismutase of Escherichia coli.
abstract: The discovery of superoxide dismutase (CuZnSOD) within the periplasms of several Gram-negative pathogens suggested that this enzyme evolved to protect cells from exogenous sources of superoxide, such as the oxidative burst of phagocytes. However, its presence in some non-pathogenic bacteria implies that there may be a role for this SOD during normal growth conditions. We found that sodC, the gene that encodes the periplasmic SOD of Escherichia coli, is repressed anaerobically by Fnr and is among the many antioxidant genes that are induced in stationary phase by RpoS. Surprisingly, the entry of wild-type E. coli into stationary phase is accompanied by a several-hour-long period of acute sensitivity to hydrogen peroxide. Induction of the RpoS regulon helps to diminish that sensitivity. While mutants of E. coli and Salmonella typhimurium that lacked CuZnSOD were not detectably sensitive to exogenous superoxide, both were killed more rapidly than their parent strains by exogenous hydrogen peroxide in early stationary phase. This sensitivity required prior growth in air. Evidently, periplasmic superoxide is generated during stationary phase by endogenous metabolism and, if it is not scavenged by CuZnSOD, it causes an unknown lesion that augments or accelerates the damage done by peroxide. The molecular details await elucidation.
authors.affiliation: Department of Microbiology, University of Illinois, Urbana 61801, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Gort
authors.forename: D M
authors.initials: DM
authors.lastname: Ferber
authors.forename: J A
authors.initials: JA
authors.lastname: Imlay
mesh_terms: D000483:Alleles; D001426:Bacterial Proteins / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins; D005838:Genotype; D006861:Hydrogen Peroxide / Q000378:metabolism; D018384:Oxidative Stress; D019897:Periplasm / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids; D011993:Recombinant Fusion Proteins; D012486:Salmonella typhimurium / Q000201:enzymology; D012808:Sigma Factor / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D014969:Xanthine Oxidase / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D003300:Copper; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; C116114:sodC protein, E coli; D014969:Xanthine Oxidase; D001616:beta-Galactosidase; D015032:Zinc