Fig. 1.

P. aeruginosa is capable of natural transformation in continuous-flow biofilms. Carbenicillin- or gentamicin-resistant transformants obtained from continuous-flow biofilms of PAO1 in Tygon tubing. For (a) pUCPSK (Carb^R) was added to the media influent (at a final concentration of 1 µg ml⁻¹ with flow rate of 80 µg min⁻¹) with either the biofilm biomass or effluent harvested and plated on carbenicillin selective agar plates on the indicated day. For (b) sterile gDNA or total eDNA obtained from PAO1_GFP (Gm^R) (at a final concentration of 0.1 mg ml⁻¹ with flow rate of 80 µg min⁻¹) was added to the media influent and the biofilm biomass harvested and plated on gentamicin selective agar plates after 5 days. The mean of each set of technical triplicates was calculated to give an n≥4, which is presented as mean±sem (* P <0.05; Mann–Whitney U-test compared to gDNA).