FIG. 4.

(A) EnvZ is required for SPI2 induction by EDTA. An envZ mutant exhibited basal levels of ssaG expression upon treatment with EDTA, in contrast to the wild type and an ackA-pta mutant, in which ssaG expression was increased upon treatment with EDTA. (B) EnvZ is required for medium shift control of ssaG. Shifting wild-type Salmonella from a rich medium (LB medium) to an acidic minimal medium (M9 pH 5 medium) resulted in ssaG-gfp expression in wild-type and ackA-pta backgrounds but not in an envZ mutant.