title: Compensatory role of PspA, a member of the phage shock protein operon, in rpoE mutant Salmonella enterica serovar Typhimurium.
abstract: Sigma(E) is an alternative sigma factor that responds to and ameliorates extracytoplasmic stress. In Salmonella enterica serovar Typhimurium (S. Typhimurium), sigma(E) is required for oxidative stress resistance, stationary-phase survival and virulence in mice. Microarray analysis of stationary-phase gene expression in rpoE mutant bacteria revealed a dramatic increase in expression of pspA, a member of the phage shock protein (psp) operon. The psp operon can be induced by filamentous bacteriophages or by perturbations of protein secretion, and is believed to facilitate the maintenance of proton motive force (PMF). We hypothesized that increased pspA expression may represent a compensatory response to the loss of sigma(E) function. Increased pspA expression was confirmed in rpoE mutant Salmonella and also observed in a mutant lacking the F(1)F(0) ATPase. Alternatively, expression of pspA could be induced by exposure to CCCP, a protonophore that disrupts PMF. An rpoE pspA double mutant strain was found to have a stationary-phase survival defect more pronounced than that of isogenic strains harbouring single mutations. The double mutant strains were also more susceptible to killing by CCCP or by a bactericidal/permeability-increasing protein (BPI)-derived anti-microbial peptide. Using fluorescence ratio imaging, differences were observed in the Deltapsi of wild-type and rpoE or pspA mutant bacteria. These findings suggest that pspA expression in S. Typhimurium is induced by alterations in PMF and a functional sigma(E) regulon is essential for the maintenance of PMF.
authors.affiliation: Departments of Laboratory Medicine and Microbiology, University of Washington School of Medicine, Seattle, WA 98195, USA.
authors.forename: Lynne A
authors.initials: LA
authors.lastname: Becker
authors.forename: Iel-Soo
authors.initials: IS
authors.lastname: Bang
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Crouch
authors.forename: Ferric C
authors.initials: FC
authors.lastname: Fang
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000378:metabolism; D002470:Cell Survival; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D009876:Operon; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D007476:Ionophores; D012808:Sigma Factor; D014157:Transcription Factors; C069816:phage shock protein, Bacteria; C063202:sporulation-specific sigma factors; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012321:DNA-Directed RNA Polymerases