FIG. 4.

The growth phase influences the expression of lacZ transcriptional fusions to T3SS genes. β-Galactosidase activity levels were measured in strains containing single-copy transcriptional lacZ fusions to the structural genes vcsRTCNS2, vspD, vcsJ2, and vcsVUQ2, the vopF gene (encoding an effector protein), and the putative transcriptional regulators A33_1675 and A33_1664. The promoterless lacZ fusion was integrated as a control for the basal level of reporter gene expression. Strains were grown in LB medium at 37°C to exponential phase (dark gray bars) or to stationary phase (white bars). The data shown represent the results of one experiment. Experiments were performed twice using three individual colonies each time and produced similar results. Note that the two graphs have different y-axis scales.