FIG. 3.

Transcriptional repression of srfABC by PhoP. Expression levels of srfB (A) and prgH and ssaV (B) were monitored with lacZ transcriptional fusions. Strains carrying the indicated mutations were cultured in the following media: LB medium for SPI-1 induction; LPM for SPI-2 induction; and LB medium containing EDTA for Mg²⁺ chelation. The β-galactosidase activities shown were measured in stationary-phase cultures, but similar results were obtained in exponential cultures. The data represent the averages and standard deviations from two experiments. wt, wild type.