Effect of acyl-HSL addition or early expression of LasR or RhlR on the transcription of selected P. aeruginosa quorum-controlled genes in logarithmic and stationary phase. Top panels, transcript abundances as determined by real-time PCR normalized to the transcript levels of the lasR, rhlR mutant in logarithmic phase. Error bars indicate standard errors of the mean. Concentrations of arabinose added to the cultures were as follows (from left to right, in mM): 50, 50, 7.5, 50, 1.0, 1.0, 0.1, 0.4, 0.4, 1.6. For comparison, the insets in each panel show signal specificities previously determined in a lasI, rhlI signal generation mutant without exogenous signal (dotted line), with 2 μM 3OC12-HSL (dashed line), or with both 2 μM 3OC12-HSL and 10 μM C4-HSL (solid line) . The black arrows indicate positions on the growth curve at which the corresponding cultures for real-time PCR analysis were harvested (left arrow, OD600 = 0.2; right arrow, OD600 = 2). Bottom panel, immunoblots showing the respective protein levels of LasR and RhlR.