Prolonged cold stress response of Escherichia coli O157 and the role of rpoS

Phenotypic analyses were performed using an enterohemorrhagic Escherichia coli O157 (EHEC) strain (B-1) and a commensal E. coli K-12 strain, exposed to prolonged cold stress. The EHEC E. coli O157 showed significantly (P < 0.05) higher resistance to cold stress compared to non-pathogenic E. coli K-12 DH5α. Further, it was found that RpoS sigma factor plays a significant (P < 0.05) role in the cold stress physiology of the enterohemorrhagic E. coli strain. Using comparative proteomic analysis of hypo-thermally adapted E. coli O157 wild-type and rpoS mutant strains, we identified 21 proteins that were differentially expressed upon cold temperature shifts or rpoS mutation. All identified proteins of cold post-acclimation stimulons fell into two large sub-groups: (i) stress proteins, and (ii) housekeeping proteins. This prolonged cold stress response included proteins involved in mRNA turnover, cell replication efficiency, conditional and post-synthetic modification of membrane lipid bilayers, biosynthetic processes, and the uptake of different sugars. The RpoS sigma factor had no control over the key stress proteins, polynucleotide phosphorylase and elongation factor G, in prolonged stress stimulon. However, RpoS was shown to regulate the expression of proteins involved in homeoviscous adaptation during cold shock, as well as various proteins involved in central metabolic pathways of this food-borne pathogen.