Figure 5. PQS reduces the intracellular ROI levels.

The median of fluorescence intensity (MFI) of 50,000 log phase grown cells treated with 20 µM H₂DCFDA is given. PQS was added to log phase grown PAO1 wild-type and pqsA mutant cultures at concentrations of 0, 50 and 100 µM PQS, respectively followed by an 1 h incubation period prior to FACS analysis. In contrast to PQS addition, the addition of at least equimolar concentrations of the biologically less active PQS precursor heptyl-4-hydroxy-quinoline (HHQ) or the iron chelator dipyridyl did not show a clear reduction of the ROI levels (data not shown). The assays were performed three times with independent cultures, the addition of PQS reduced the MFI significantly as determined by t-test (p<0.05).