FIG. 4.

Effects of global regulatory systems on the expression of the SsrAB virulon. The expression of representative genes of the SsrAB virulon was analyzed in strains defective in various regulatory systems, as indicated. Reporter fusions for sifA and sseJ were used to represent transcriptional units outside of SPI2, while sseA represents a transcriptional unit within SPI2. Reporter fusions were analyzed in the WT strain or in a phoP, ompR, slyA, or sirA deletion background. The strains were subcultured in noninducing minimal medium (PCN medium-25 mM Pi, pH 7.4; red) or under SPI2-inducing conditions (PCN medium-0.4 mM Pi, pH 5.8; all other histograms). Representative growth curves are shown in the bottom panel, and all reporter strains showed similar growth characteristics. Cells were harvested at various time points, and equal amounts of cells, as adjusted by OD₆₀₀, were lysed for the quantification of Luc activities. The quantification of reporter activities was performed as described for Fig. 2, and means and standard deviations for triplicate assays are shown.