FIG 2 .

AHLs and RhlR mediate QS in some LasR-null clinical isolates. (A and B) AHL dependence of elastase and pyocyanin production. LasR-null mutants were grown in broth with (light bars) or without (dark bars) 20 µg/ml AiiA lactonase. In all cases, AiiA lactonase-grown cultures did not have measurable signals after 18 h. We measured production of elastase (A) and pyocyanin (B) from these cultures after 18 h of growth. PAO1 (red) and an AHL QS-deficient strain, mutant strain PAO1 ΔlasR ΔrhlR ΔqscR (ΔRRR) (blue), are shown for comparison. Elastase activity is shown in arbitrary units. (C) RhlR activity in LasR-null isolates. We electroporated AHL-responsive isolates with an RhlR-responsive rhlA-gfp reporter and measured fluorescence at 18 h. Fluorescence per cell is reported for clinical isolates (dark bars) with PAO1 (red), PAO1 ΔlasR, and PAO1 ΔRRR (blue) shown for comparison. Isolate E183, which demonstrated wild-type function, is also included. Growth with AiiA lactonase (light bars) abrogated the fluorescence in most cases. (D) Temporal profile of RhlR activation of the rhlA-gfp reporter. Strains E42 (closed circles), E131 (closed triangles), and E165 (open circles) are shown. PAO1 (closed squares) is shown in red, and PAO1 ΔlasR (inverted triangles) is shown in blue. In all panels, error bars show standard errors for results from four independent measurements. *, a statistically significant decrease (P < 0.05) in production of elastase (A), pyocyanin (B), or GFP (C) in the presence of AiiA, compared to the buffer control (two-tailed t test).