Role of Phage Shock Protein in Recovery of Heat-injured Salmonella

Sublethally heat-injured cells of Salmonella in food can recover under favorable conditions, leading to foodborne illness. To elucidate the molecular mechanism of recovery from heat injury, the global changes in gene transcription of Salmonella Typhimurium were investigated in previous study. In this study, the functions of genes involved in phage shock response (viz., phage shock protein (psp) genes), the transcription levels of which were found in previous study to be increased during recovery from heat injury, were investigated in recovering cells. The increase in pspABCDEFG transcription levels during the recovery process was confirmed by qRT-PCR. To understand the role of psp genes in heat injury recovery, a pspA deletion mutant (ΔpspA) and a pspA-overexpressing strain (S. Typhimurium pBAD30/pspA (+) ) were constructed. ΔpspA showed slightly lower viable counts and membrane potential than those of the wild-type strain during recovery. On the other hand, there was no significant difference in the viable counts between S. Typhimurium pBAD30/pspA (+) and the control strains S. Typhimurium pBAD30/pspA (-) and S. Typhimurium pBAD30 (+) during recovery. It would seem that a lack of PspA protein alone somewhat affects the recovery of S. Typhimurium from heat injury, but overexpression of PspA alone is not sufficient to overcome this effect.