Figure 4

β-Galactosidase assays showing expression profile of ppoR and the QS system genes of P. putida WCS358 and RD8MR3. Bacterial cultures were started with an initial inoculum of 5 × 10⁶ CFU per ml in 20 ml of minimal medium (M9-Cas) and β-Galactosidase activities were measured at different stages of growth. The growth curves of different mutants and the wild type strain are indicated in each graph. All experiments were performed in triplicate and the mean values of each time point along with standard deviations are shown in each graph. All the graphs were plotted using SigmaPlot version10.0. (a, b, and c) ppuI, ppuR and rsaL promoter activities of P. putida WCS358 in wild type and WCS358PPOR using plasmids pPUI220, pPUR220 and pRSA220. Paired t-test analysis of ppuI promoter activities revealed a significant difference between the mean values of wild type and WCS358PPOR at 7 hours of growth (p value 0.0184; t = 7.268 df = 2) at P < 0.05 significance level. (d) pprI promoter activity in P. putida RD8MR3 wild type and RD8MR3PPOR with the plasmid pMPpprIprom. (e) ppoR promoter activity in P. putida WCS358 wild type, ppuI knock-out (IBE5), ppuR (IBE2) and rsaL (IBE3) mutants with the plasmid pPpoR2. Anova analysis of sample means followed by Dunnett's multiple comparison test revealed that there is a significant difference between the means of wild type and IBE5 at P < 0.05 significance level at 4, 6 and 24 hours growth [F(3,8) = 6.278, F(3,8) = 22.97 and F(3,8) = 16.37 respectively] (f) ppoR promoter activity in P. putida RD8MR3 wild type, pprI (RD8MR3PPRI) and pprR (RD8MR3PPRR) mutants with the plasmid pPpoR1. β-gal, β-galactosidase; OD600, optical density at 600 nm; MU, Miller Units.