Fig. 3.

Temperature-dependent expression of rhlR in P. aeruginosa depends on the transcription of the rhlAB-R operon at 37 °C. (A) Diagram of plasmid pSC1002, which encodes for an rhlR–lacZ transcriptional fusion (containing the four rhlR immediately upstream promoters), and the expression of this rhlR–lacZ fusion in P. aeruginosa PAO1 at 30 °C (gray line) and 37 °C (black line). (B) Expression of rhlR from the rhlA promoter in strain PW6882, which contains an in-frame Tn9-lacZ insertion inside rhlR (SI Appendix, Table S1) at 30 °C (white bars) and 37 °C (gray bars). The first set of bars at both temperatures represents the basal expression of chromosomal rhlR; the second set of bars corresponds to the expression of this gene in the presence of the promoter in strain PW6882, with cloning vector pUCP20 (used as control of rhlR LasR-dependent expression); and the third set of bars at each temperature represents the expression with plasmid pGMYC (SI Appendix, Table S1) expressing rhlR in trans. *P < 0.05 by Student t test. (C) RhlR concentration was determined by Western blot analysis, expressed from plasmid pGMYC. The samples were the same as those used for β-galactosidase determination in B.