Fig. 2.

Pel affects the morphology of PA14 biofilm streamers. (A–C) Representative overlaid phase-contrast (bacterial cells) and red fluorescence (eDNA) images of the biofilm streamers formed by P. aeruginosa PA14 Pel-deficient (ΔpelE) (A), WT (B), and Pel-overproducing (ΔwspF) (C) cells attached to a 50-µm pillar after 15 h of continuous flow of a dilute bacterial suspension at U = 2 mm/s. The images are representative of the streamer morphology obtained with the different mutant strains. (D) Length of streamers after 15 h (filled symbols) and 22 h (open symbols) of continuous flow, measured from fluorescence images for ΔpelE, WT, and ΔwspF strains. (E) Diameter of streamers in the vicinity of the pillar (150 µm from the pillar, $d_{150})$ (green triangles) and in the downstream region (400 µm from the pillar, $d_{400})$ (blue circles) after 15 h (filled symbols) and 22 h (open symbols) of continuous flow, measured from fluorescence images for the three strains. (F) Green fluorescence intensity of streamers, ${\overline{I}}_{\text{Pel}}$, corresponding to the Pel content, for the three strains after 24 h. (G) Red fluorescence intensity of streamers, ${\overline{I}}_{\text{str}}$, corresponding to the eDNA content, as a function of time (red squares, ΔpelE; blue circles, WT; green triangles, ΔwspF). (H) Red fluorescence intensity measured on the pillar surface, ${\overline{I}}_{\text{pill}}$, as a function of time for the same suspensions as G. (I) Coverage of the bottom surface of the channel, $C_{\text{surf}}$, as a function of time for the same suspensions as G and H. Error bars represent the SEM.