Envelope Stress Activates Expression of the Twin Arginine Translocation (Tat) System in Salmonella

The twin arginine translocation system (Tat) is a protein export system that is conserved in bacteria, archaea, and plants. In Gram-negative bacteria, it is required for the export of folded proteins from the cytoplasm to the periplasm. In Salmonella, there are 30 proteins that are predicted substrates of Tat, and among these are enzymes required for anaerobic respiration and peptidoglycan remodeling. We have demonstrated that some conditions that induce bacterial envelope stress activate expression of a ΔtatABC-lacZ fusion in Salmonella enterica serovar Typhimurium. Particularly, the addition of bile salts to the growth medium causes a 3-fold induction of a ΔtatABC-lacZ reporter fusion. Our data demonstrate that this induction is mediated via the phage shock protein (Psp) stress response system protein PspA. Further, we show that deletion of tatABC increases the induction of tatABC expression in bile salts. Indeed, the data suggest significant interaction between PspA and the Tat system in the regulatory response to bile salts. Although we have not identified the precise mechanism of Psp regulation of tatABC, our work shows that PspA is involved in the activation of tatABC expression by bile salts and adds another layer of complexity to the Salmonella response to envelope stress. IMPORTANCE Salmonella species cause an array of diseases in a variety of hosts. This research is significant in showing induction of the Tat system as a defense against periplasmic stress. Understanding the underlying mechanism of this regulation broadens our understanding of the Salmonella stress response, which is critical to the ability of the organism to cause infection.