Interplay of cold shock protein E with an uncharacterized protein, YciF, lowers porin expression and enhances bile resistance in Typhimurium.

Bacterial cold shock proteins (CSPs) function as RNA chaperones. To assess CSP's roles in the intracellular human pathogen Typhimurium, we analyzed their expression in varied stress conditions. We found that cold shock protein E ( or STM14_0732) is up-regulated during bile salt-induced stress and that an Typhimurium strain lacking (Δ) displays dose-dependent sensitivity to bile salts, specifically to deoxycholate. We also found that an uncharacterized gene, (STM14_2092), is up-regulated in response to bile stress in WT but not in the Δ strain. Complementation with WT CspE, but not with a F30V CspE variant, abrogated the bile sensitivity of Δ as did multicopy overexpression of Northern blotting experiments with rifampicin disclosed that the regulation of expression is, most likely, due to the RNA-stabilizing activity of CspE. Importantly, electrophoretic mobility shift assays indicated that purified CspE, but not the F30V variant, directly binds mRNA. We also observed that the extra-cytoplasmic stress-response (ESR) pathway is augmented in the bile-treated Δ strain, as judged by induction of RpoE regulon genes (, , and ) and downstream ESR genes (, , and ). Moreover, the transcript levels of the porin genes, , , and , were higher in bile salts-stressed Δ and correlated with higher intracellular accumulation of the fluorescent DNA stain bisBenzimide H 33258, indicating greater cell permeability. In conclusion, our study has identified YciF, a CspE target involved in the regulation of porins and in countering bile stress in Typhimurium.