Transcriptional activity of rhlG under hyperosmotic stress. Promoter activity was followed by measuring luminescence from strains harbouring pAB134, which contain rhlG::luxCDABE transcriptional fusion. Activity was measured in P. aeruginosa PAO1 wildtype with or without NaCl (respectively white and black squares) and supplemented with 1 mM GB in presence of NaCl (black circles) (A). Hyperosmotic stress effect on rhlG activity was followed in PA6358 (rpoN mutant, diamonds) compared to wildtype (squares) during the same set of experiments (B). Hyperosmotic stress effect on prrhlG activity was followed in PAOU (algU mutant, triangles) compared to wildtype (squares) during the same set of experiments (C). Activity is expressed in Relative Units of Luminescence per 0.5 second in function of time growth. Gain for luminescence detection was automatically set for each experiment. Results are representative of 2 complete experiments and of several additional experiments with fewer time points, standard deviations were < 7% for all values. Curve without symbol in panel A: growth curve of PAO1 with 0.5 M NaCl (S) or not (C).