Role of the alternative sigma factors σ E and σ S 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 s E and s S , 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 s E -and s S -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 6C) 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 a w ) containing 6 % NaCl and at refrigeration temperature, both sigma factors were important for maximum survival but s S played the dominant role. Analysis of the metabolic activity of starved populations at 4.5 and 37 6C revealed significantly (P<0.001) elevated electron-transport system activity in mutants in rpoE and rpoS, indicating a role for s E -and s S -regulated genes in maintaining energy homeostasis. Together these data demonstrate that s E and s S are important for survival of S. Typhimurium in conditions encountered during food processing and that the relative contribution of s E and s S is critically dependent on the precise nature of the stress.

Thermal Resistance and Gene Expression of both Desiccation-Adapted and Rehydrated Salmonella enterica Serovar Typhimurium Cells in Aged Broiler Litter

“…Genes that are upregulated under desiccation stress. In Salmonella, the rpoS gene encodes an alternative sigma factor ( S /RpoS) that initiates the transcriptions of a series of genes and acts as a master regulator required for survival under harsh conditions (25,26). In the present study, in agreement with the known role of the rpoS gene in the general stress response, the rpoS gene was found to be significantly upregulated following desiccation in aged broiler litter (P Ͻ 0.05).…”

The Divergent AmoC 3 Subunit of Ammonia Monooxygenase Functions as Part of a Stress Response System in Nitrosomonas europaea

“…It is generally accepted that most bacteria respond to starvation through cellular changes contributing to increased resistance to a variety of stressors (e.g., heat, pH, oxidative stress, osmotic stress), that these changes promote survival during starvation (16,33,35,36), and that they occur during transition into stationary phase (15,24). Regulation of this response includes the function of the S sigma factor in the Gammaproteobacteria (27), the stringent response mediated by the small molecule ppGpp (38), and induction of pathways that deal specifically with C, N, or P limitation (40).…”

“…Analogous to what is seen for stress-resistant spores, these physiological changes protect starved nondifferentiating bacteria that exist in an otherwise vulnerable state. In the Gammaproteobacteria, arguably the most well-studied group of organisms with respect to their starvation response, the physiological changes that occur during starvation are regulated in part by the S , E , and 32 sigma factors that control the expression of stress response genes during starvation (20,27,33). Overall, on the order of 20 to 40 starvationinduced proteins have been identified in Escherichia coli (13,31) and other bacteria (5,15,37,40).…”

Stress Responses of Foodborne Pathogens and Implications in Food Safety

“…Cross-protection has been found to be mediated by the rpoS gene. In some bacteria, the rpoS gene encodes an alternative sigma factor (σ S /RpoS) that acts as a master regulator needed for the survival under stressful conditions [17]. The rpoS gene has been identified to be involved in the cross-protection of desiccation-adapted Salmonella typhimurium against high temperatures [18].…”