Fig. 5: Sub-MIC antibiotics fail to stimulate biofilm formation in a sigX mutant.

a Sub-MIC cefixime, tobramycin, and thiostrepton do not stimulate biofilm formation in a sigX mutant (N = 3). Notably, loss of sigX greatly increases the baseline biofilm formation in the untreated control. A two-way ANOVA followed by Šídák’s multiple comparisons test was performed between the biofilm formation data for PAO1 and the sigX::FRT mutant for each antibiotic in a. Each data point is shown at individual circles, where black circles represent PAO1 and white circles represent sigX::FRT. Cef cefixime, Ts thiostrepton, Tob tobramycin. b Supplementing 0.1% Tween 80 into the media restores biofilm stimulation for a sigX mutant but not an oprF mutant (N = 2). A two-way ANOVA followed by Tukey’s multiple comparisons test was performed for the biofilm formation data in b. ns not significant, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. For both figures, three technical replicates were performed for each biological replicate and data from a representative biological replicate is shown. The graphs show the maximum amount of biofilm observed from a dose-response assay (such as those shown in Fig. 1) for each antibiotic/strain. Planktonic growth (OD₆₀₀, yellow) and biofilm (A₆₀₀, purple) are reported as percentage of the untreated control. Error bars represent the standard deviation. Source data are provided in Supplementary Data Set 1.