Role of Sigma B Factor in the Alkaline Tolerance Response of Listeria monocytogenes 10403S and Cross-Protection against Subsequent Ethanol and Osmotic Stress

Abstract

Many of the considerable abilities of Listeria monocytogenes to persist and grow in a wide range of adverse environmental conditions are thought to be at least partly under the control of the alternative sigma factor (sigmaB), encoded by the sigB gene. However, little is known about the role of this master regulon in the impressive ability of Listeria to persist and grow under conditions of alkaline pH. In this study, Northern blot analysis of parent Listeria mRNA revealed that alkali adaptation (pH 9.5 for 1 h) significantly increased the expression of sigB-derived mRNA. The study included a comparison of the relative survival of mid-exponential populations of adapted and nonadapted parent type (sigmaB expressing) and mutant (not sigmaB expressing, deltasigB) Listeria strains during subsequent alkaline (pH 12.0), osmotic (25% NaCl, wt/vol), or ethanol (16.5%) stress. Alkali-adapted parent strains were more resistant to pH 12.0 than were adapted deltasigB type strains, but both alkali-adapted parent and deltasigB strains were more resistant to pH 12.0 than were nonadapted strains. Alkali-adapted parent strains were more resistant to osmotic stress than were adapted deltasigB type strains. No significant differences in viability were observed between alkali-adapted parent and deltasigB strains after ethanol stress, suggesting that cross-protection against osmotic stress is mediated by sigmaB whereas cross-protection against ethanol is sigmaB independent. Overall, alkali-induced cross-protection against osmotic and ethanol challenges may have serious implications for food safety and human health because such stress conditions are routinely used as part of food preservation and surface cleaning processes.

Roles of Four Putative DEAD-Box RNA Helicase Genes in Growth of Listeria monocytogenes EGD-e under Heat, pH, Osmotic, Ethanol, and Oxidative Stress Conditions

“…Whole-genome microarray studies have shown 714, 411, and 355 genes of L. monocytogenes to be differentially transcribed under heat (58), cold (10), and alkali stresses (20), respectively, compared with control growth conditions. Mutational analyses have confirmed the role of alternative sigma factors in the bacterium's tolerance to all these, as well as osmotic, acid, oxidative, and ethanol stresses (9,12,18,19,41,(47)(48)(49)60). In addition, the involvement of approximately 30 other factors in the tolerance of L. monocytogenes to these stresses has been reported (54).…”

Transcriptome Analysis of Alkali Shock and Alkali Adaptation inListeria monocytogenes10403S

“…AS also upregulated 4 regulatory proteins (RsbV, RsbW, RsbX, and RsbS) involved in the posttranslational regulation of the activity of sigB, suggesting multilevel modulation of the activities of this key regulon (Supplemental Table S1). Thus, the alkaliinduced upregulation of RsbV and RsbW observed in this study is probably responsible, at least in part, for the observed upregulation of sigB, itself the central switch in the rapid activation of a range of mechanisms that allow Listeria to survive the alkali stress challenges posed in the human gastrointestinal tract and alkali-based disinfectants used in foodprocessing systems (Giotis et al, 2008a).…”

“…The significance of this operon as a central mechanism in the sophisticated adaptive mechanisms to stress has been highlighted in a wide range of bacteria (Karlin et al, 2004;Satorhelyi, 2004). In L. monocytogenes, it is involved in resistance against alkali, oxidative, osmotic, heat, bile, and acid stress (Ferreira et al, 2004;Moorhead and Dykes, 2004;Sue et al, 2004;Giotis et al, 2008a) and is also important in virulence and the ability to invade host cells (Kim et al, 2005;Rauch et al, 2005;Garner et al, 2006). As might be expected of such an important regulon, sigB is itself subject to a complex regulatory system, and this study observed that AS induced significant upregulation of three genes (lmo0889, lmo0891, and lmo0892) that encode for proteins involved in the regulation of sigB.…”

“…Concerns are increased by the ability of Listeria to become stress hardened by sublethal concentrations of alkaline detergents, making the pathogen capable of resisting previously lethal alkali-, ethanol-, osmotic-, or thermal-based cleaning procedures Beuchat, 2002a, 2002b;Giotis et al, 2008a), and contributing to reported failures to eradicate Listeria from foodprocessing environments (Sharma et al, 2003). The ability to resist mild alkaline pH values may also contribute to the pathogenicity of Listeria by increasing its survival in alkali conditions in phagolysosomes (Segal et al, 1981) and pancreatic secretions (Maurer et al, 2005).…”

Ecological attributes of foodborne infections

“…25,26 A similar sigma factor σB, encoded by the sigB gene is the responsible mediator for the resistance of Gram-positive bacteria e.g., S. aureus, L. monocytogenes and Bacillus spp in many adverse environmental conditions. 27 For Escherichia coli, global stress response is triggered by the alternative sigma factor RpoS and this may result in tolerance to homologous or heterologous (i.e., cross tolerance) stresses. For instance, cells starved for carbon become resistant to hydrogen peroxide, high temperature and low pH.…”