FIG 3.

RpoN is essential for the expression of the PA5530-lacZ reporter. Positioned 93 bp upstream of the PA5530 ORF is a sequence resembling a −24/−12 promoter (GG-N₁₀-GC). Replacement of the conserved “GG” dinucleotide of the −24 element with “AA” in the PA5530-lacZ reporter (denoted AA-N₁₀-GC) reduced its expression by >95% in P. aeruginosa PAO1. Additionally, expression of the PA5530-lacZ reporter was null in an rpoN::Ω-Km derivative of P. aeruginosa PAO1. Note that all strains were grown in nutrient broth no. 2 (Oxoid) to an OD₆₀₀ of 0.3 and then induced with 20 mM α-KG. LacZ activity was measured at 90 min postinduction. Data points represent mean values ± SD (n = 3). Analysis of variance was performed by using Dunnett's post hoc test (α-value of 0.05) to identify significant changes (P < 0.0001), which are marked (asterisk).