RpoS-Mediated Stress Response Does Not Impact the Rate of T7 Bacteriophage-Induced Lysis of Escherichia coli

SUMMARY The alternative sigma factor RpoS is proposed to confer cross-protection against bacteriophage T7-mediated lysis in Escherichia coli after exposure to antibiotics. In E. coli, RpoS is a regulatory protein that modulates the expression of general stress response genes upon exposure to environmental stress. This response may prime a response against secondary environmental stressors. Previous studies found that pre-treatment with sub-lethal concentrations of antibiotics as a primary stressor can delay T7 bacteriophage-induced lysis. We hypothesized that the delayed lysis observed in E. coli pre-treated with antibiotics is the result of cross-protection conferred by RpoS activation, with T7 bacteriophage infection as the secondary stressor. We used minimum inhibitory concentration assays to determine the sub-lethal kanamycin and ampicillin concentrations for the wild-type and rpoS knockout mutant (EEKA18-1) E. coli. After pre-treating the cells with sub-lethal concentrations of antibiotics, we performed an OD-based real-time T7 bacteriophage lysis assay to generate lysis curves of each treatment (n=3). The EEKA18-1 rpoS knockout mutant exhibited similar lysis curves to the wild-type cells. Contrary to previous findings, our results suggest that pre-treatment with sub-lethal concentrations of kanamycin and ampicillin does not delay T7 bacteriophage-induced lysis in wild-type cells. This indicates that the RpoS-mediated general stress response may not confer cross-protection against T7 bacteriophage infection.