Fig. (4) Relative expression levels of the genes lasI, rhlI, rhlC, pqsH and of the operons rhlAB and pqsABCDE in P. aeruginosa PAO1 submitted to 0.5 M osmotic shock without glycine betaine (GB) or in its presence. RNAs were extracted after 20 h of growth and the expression levels were determined by qRT-PCR, relatively to the expression in PPGAS medium without stress. Primers internal to rhlA, pqsC and pqsE were used to quantify rhlAB and pqsABCDE mRNAs. Relative values lower than 1 indicate reduction of gene expression upon stress (e.g. a value of 0.5 reveals that the mRNA level was divided by 2 in hyperosmotic condition). 16S rRNA was used as endogenous control to normalize the RNA input and reverse transcription efficiency. PCR reactions were performed in triplicate and the standard deviations were lower than 0.15 C_T.