Figure 2. Filamentation is associated with conditions that strongly stimulate PhoQ/PhoP.

(a) Measurement of phoPQ promoter activity from a P_phoPQ-yfp transcriptional reporter in wild-type (TIM148), ΔphoQ (TIM229) and ΔmgrB (AML22) strains in minimal medium at indicated Mg²⁺ concentration. For wild-type cells grown in the presence of antimicrobial peptide C18G, C18G was added to a final concentration of 9 μg ml⁻¹. Cells were grown until an OD₆₀₀=0.2–0.3 and fluorescence was measured by microscopy. Data represent means and s.d.'s from at least three independent experiments. (b) Cellular morphology of wild-type (TIM92), ΔmgrB (AML20), ΔmgrB ΔphoQ (AML17) and ΔmgrB ΔqueE (JNC21) cells grown in minimal medium with no added Mg²⁺. Scale bar, 5 μm.