title: Increased mutability by oxidative stress in OxyR-deficient Escherichia coli and Salmonella typhimurium cells: clonal occurrence of the mutants during growth on nonselective media.
abstract: Escherichia coli and Salmonella typhimurium strains deficient in the OxyR-regulated adaptive response to oxidative stress were used to study the mode in which spontaneous SOS-dependent mutations are generated in a distressed bacterial population. When assayed on supplemented selective medium, the E. coli strain IC3821 (trpE65), carrying the delta oxyR30 mutation and containing the plasmid pRW144 (mucA/B), showed a frequency of spontaneous Trp+ revertants similar to that of the oxyR+ control. Instead, the IC3821 strain exhibited an enhancement in the clonal occurrence of spontaneous revertants arising at random during growth on a nonselective medium. A similar enhancement was observed for the S. typhimurium strain TA4125 (hisG428 delta oxyR2). The mutator effect observed in oxyR- cells would be induced by an increased background of reactive oxygen species; it provides a model for studying the mutability of a cell population constantly exposed to mutation-inducing agents. In the IC3821 strain, revertants were induced by t-butyl hydroperoxide with higher efficiency than in oxyR+. We suggest that strain IC3821 could be useful for the detection of SOS-dependent mutagenesis induced by chemical oxidants.
authors.affiliation: Instituto de Investigaciones Citológicas, Fundación Valenciana de Investigaciones Biomédicas, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Blanco
authors.forename: G
authors.initials: G
authors.lastname: Herrera
authors.forename: A
authors.initials: A
authors.lastname: Urios
mesh_terms: D000220:Adaptation, Biological; D001426:Bacterial Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D029968:Escherichia coli Proteins; D017353:Gene Deletion; D008957:Models, Genetic; D016296:Mutagenesis / Q000235:genetics*; D018384:Oxidative Stress / Q000235:genetics*; D010545:Peroxides / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000494:pharmacology; D012097:Repressor Proteins; D013014:SOS Response, Genetics / Q000235:genetics; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics*; D012641:Selection, Genetic; D014157:Transcription Factors; D020122:tert-Butylhydroperoxide
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D010545:Peroxides; D017382:Reactive Oxygen Species; D012097:Repressor Proteins; D014157:Transcription Factors; C499299:oxyR protein, E coli; D020122:tert-Butylhydroperoxide