title: Role of the alternative sigma factors sigmaE and sigmaS in survival of Salmonella enterica serovar Typhimurium during starvation, refrigeration and osmotic shock.
abstract: The ability of Salmonella enterica serovar Typhimurium to survive environmental stress requires specific, coordinated, responses, which induce resistance to the stress condition. This study investigated the relative contribution of sigmaE and sigmaS, the sigma factors regulating extracytoplasmic and general stress response functions, respectively, to survival at low temperature and also in media of differing osmotic strength, conditions relevant to food preservation. To determine if low-temperature storage is a signal for sigmaE- and sigmaS-mediated survival, the ability of S. Typhimurium rpoE, rpoS and rpoE/rpoS mutants to survive in a saline starvation-survival model at a refrigeration temperature (4.5 degrees C) was examined. Under these conditions, the rpoE mutant was significantly (P<0.05) compromised compared to the parent and to an rpoS mutant. The double mutant in rpoE and rpoS displayed a cumulative defect in survival. In hyperosmotic environments (low aw) containing 6 % NaCl and at refrigeration temperature, both sigma factors were important for maximum survival but sigmaS played the dominant role. Analysis of the metabolic activity of starved populations at 4.5 and 37 degrees C revealed significantly (P<0.001) elevated electron-transport system activity in mutants in rpoE and rpoS, indicating a role for sigmaE- and sigmaS-regulated genes in maintaining energy homeostasis. Together these data demonstrate that sigmaE and sigmaS are important for survival of S. Typhimurium in conditions encountered during food processing and that the relative contribution of sigmaE and sigmaS is critically dependent on the precise nature of the stress.
authors.affiliation: Division of Veterinary Pathology, Infection and Immunity, School of Clinical Veterinary Science, University of Bristol, Langford, Bristol BS40 5DU, UK.
authors.forename: Alisdair
authors.initials: A
authors.lastname: McMeechan
authors.forename: Mark
authors.initials: M
authors.lastname: Roberts
authors.forename: Tristan A
authors.initials: TA
authors.lastname: Cogan
authors.forename: Frieda
authors.initials: F
authors.lastname: Jørgensen
authors.forename: Andrew
authors.initials: A
authors.lastname: Stevenson
authors.forename: Claire
authors.initials: C
authors.lastname: Lewis
authors.forename: Gary
authors.initials: G
authors.lastname: Rowley
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Humphrey
mesh_terms: D001426:Bacterial Proteins / Q000502:physiology*; D009997:Osmotic Pressure; D012034:Refrigeration; D012486:Salmonella typhimurium / Q000502:physiology*; D012808:Sigma Factor / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; C063202:sporulation-specific sigma factors