RpoS function in Salmonella Typhimurium LT2 monitored in a skim milk model food

In Salmonella Typhimurium, the stationary phase sigma factor RpoS regulates the expression of genes associated with adaptation, survival, and virulence. Expression of rpoS is known to be under environmental control and yet, to date, there have been no studies that assess the expression of this global regulator in real food systems. Skim milk represents a useful model food; using an spvRA::luxCDABE reporter construct, we have determined RpoS availability from an inoculum of Salmonella Typhimurium LT2. We report that RpoS activity increases exponentially at the end of the logarithmic phase of growth, consistent with data from nutrient media.