FimL, FimV and PilG are required for TFP-dependent surface sensing. Contact-dependent cAMP/Vfr-dependent gene transcription was quantified using the PaQa reporter fused to YFP. PrpoD-mKate, a constitutive promoter fusion, served as an internal control. PAO1 grown on agarose hydrogels for 4 h display higher PaQa-YFP/PrpoD-mKate fluorescence ratio (arbitrary units) compared to liquid grown cells. In contrast, the PaQa-YFP/PrpoD-mKate fluorescence ratio PAO1ΔfimL, PAO1ΔfimV, PAO1ΔfimLfimV and PAO1ΔpilG mutants was not increased in solid compared to surface growth. The individual fluorescent ratios of ~ 100 cells were determined. Shown is the mean ± SEM of 3–4 biological replicates.