FIG 4.

Role of PhoPQ and PmrAB in sensing acidic pH growth conditions. Gene expression of a plasmid-encoded pPA3552-lux reporter (A) and the chromosomally encoded PA4773::lux reporter (B) in rich LB medium adjusted to mildly acidic (pH 5.5) and neutral (pH 7) conditions is shown. Expression of both reporters is measured in wild-type and phoP::xylE (P-), phoQ::xylE (Q-), pmrA::xylE (A-), and pmrB::xylE (B-) mutant backgrounds. (C) Gene expression of oprH-lux, PA3553::lux, and PA4773::lux reporters in BM2 defined medium adjusted to pH 5.5 with a range of exogenous Mg²⁺ concentrations. (D) Despite the presence of repressing levels of 2 mM Mg²⁺, the oprH-lux, PA3553::lux, and PA4773::lux reporters are induced in BM2 defined medium adjusted to pH 5.5 compared to pH 7. All values are the averages and standard deviations from 4 replicates. Gene expression is shown at ∼7 h of growth under the respective conditions.