Relative biofilm formation ability (panels A, B) and susceptibility to the stress imposed by growth on the surface of LB solid medium supplemented or not (LB) with the indicated concentrations of methyl viologen (MV), ethanol (etOH), NaCl or SDS (SDS) (panels C,D), of strains of (panels A, C) E. coli WT (WTEc), WT expressing MtvR (WTEc+MtvR), or the Δhfq_Ec mutant (EcΔhfq), and (panels B, D) P. aeruginosa WT (WTPa), WT expressing MtvR (WTPa+MtvR), or the WT strain with the hfq_Pa gene silenced (Pahfqsil). Relative biofilm formation was estimated by dividing the total amount of biofilm formed by the total amount of biomass (see Materials and Methods section). Panels E and F show photographs illustrative of results from a single representative susceptibility experiment with the E. coli (panel E) and P. aeruginosa (panel F) strains WT (WT), WT expressing MtvR (+MtvR), and the E. coli Δhfq_Ec mutant (Δhfq), or theP. aeruginosa WT with the hfq_Pa gene silenced (hfq^sil). Susceptibilities were assessed by spot inoculation of serially diluted bacterial suspensions with an initial OD640 of 1.0. Error bars represent standard deviation of the means. Numbers above bars in panels (A) and (B) are the estimated P-values.

https://doi.org/10.1371/journal.pone.0098813.g005