Interplay of HHQ, PQS, PqsR and iron in controlling PpqsA and PpqsR activity.

Maximal promoter activity quantified in the indicated strains carrying the transcriptional fusions PpqsA::lux (A and B) or PpqsR::lux (C and D). Strains were grown in LB or in LB supplemented with 40 μM HHQ, PQS or 3-NH₂-PQS, as indicated below the graphs, in the absence (white bars) or presence (grey bars) of 100 μM FeCl₃. Diamonds indicate the pyoverdine levels in the absence (white diamonds) or in the presence (grey diamonds) of 100 μM FeCl₃. Promoter activity and pyoverdine level 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 deviations.