Effect of iron on the ability of PQS to stimulate PpqsA activity.

Maximal PpqsA promoter activity measured in the P. aeruginosa ∆4AQ strain carrying the transcriptional fusion PpqsA::lux, grown in LB (white bars) or in LB supplemented with 40 μM HHQ (light-grey bars) or 40 μM PQS (dark-grey bars), and FeCl₃ at the concentration indicated below the graph. White diamonds indicate the pyoverdine level in the supernatants of cultures grown in the presence of PQS with or without FeCl₃. Promoter activity and pyoverdine are reported as Relative Light Units (RLU) and OD₄₀₅, respectively, normalized to cell density (OD₆₀₀). The average of three independent experiments is reported with standard deviation.