Mutation design and strain background influence the phenotype of Escherichia coli luxS mutants

Previous analyses of luxS in Escherichia coli have used different strain backgrounds and design formats to produce the luxS mutation, resulting in luxS mutants with confusingly dissimilar phenotypes. This study therefore investigates the roles that strain background and mutational design strategy have upon the phenotype of the pathogenic E. coli luxS mutant. We inactivated luxS in three E. coli backgrounds: enteropathogenic E. coli E2348-69, and enterohaemorrhagic strains Sakai and NCTC12900. To investigate the influence of mutational design strategy, four mutation formats were used: antibiotic resistance insertion methodologies as previously employed, using tetracycline and chloramphenicol resistance cassettes, and non-polar strategies creating deletion and premature termination mutations. Our study showed that the E. coli luxS phenotype was markedly dependent on strain background: in some strains disruption of luxS caused significant metabolic stress or no stress at all. How the luxS mutation was constructed also shaped its phenotype: non-polar mutants were very similar to wild type, while mutations made using the antibiotic insertion methodologies produced phenotypes defective in growth and virulence. Proteomic profiling of our luxS mutants showed only a few proteins were differentially expressed and those that were altered suggested a metabolic rather than communication role for the E. coli luxS gene product.