FIG. 4.
Pyocyanin production and rhlA expression are restored to a pqsE mutant by the addition of exogenous C4-HSL. (A) The wild-type (PAO1) and pqsE mutant (PJF-QE1) strains of P. aeruginosa were grown for 18 h in LB medium supplemented with the indicated concentrations of C4-HSL. Pyocyanin was quantified as described in Materials and Methods, and data represent the average ± SD of at least three separate experiments. (B) The wild-type strain PAO1 (black bar) and pqsE mutant strain PJF-QE1 (striped bars) carrying a rhlA′-lacZ fusion on pECP60 were grown for 18 h in LB medium supplemented with the indicated concentrations of C4-HSL. β-Gal activity produced in each culture was then assayed and is presented in Miller units as the mean ± SD of results from duplicate assays from at least three separate experiments. In both panels, the numbers below the bars represent the concentration of C4-HSL. NA, no addition.