FIG. 1.

F-plasmid-containing E. coli forms complex biofilms that contain F⁺ cells with pili, colanic acid, and curli. (A) CSLM images showing time-dependent biofilm development for a natural F-plasmid-containing E. coli strain. At 2 h the bacteria formed microcolonies, which expanded into larger colonies at 8 h. By 24 h complex dense biofilms that covered most of the surface area had formed. At 48 h complex mature biofilms were observed. (B) SEM images of the biofilms at different time points. Note the conjugative pili (P) that formed connections among cells at 14 h. By 24 and 48 h, a more complex biofilm containing colanic acid (CA) and elaborated curli fibers (C) had formed. (C) Close-ups of different curli fiber structures that form cell-surface attachments at 24 h and cell-cell networks at 48 h. All experiments were repeated three times, and representative images are shown.