Fig. 1.

Influence of bacterial adhesion on microcolony morphogenesis. a Schematic of the culture chamber. Bacteria are confined between an agarose pad and a glass coverslip. b Image of a wild type E. coli microcolony after the formation of a second layer. The microcolony is fitted with an ellipse with long axis a and short axis b. Scale bar represents 20 μm. c Colony shape measured by the aspect ratio (b/a) for WT E. coli and mutants impaired in adhesive molecules as a function of the number of bacteria in the microcolony. d When microcolonies exceed a certain size (N_2D/3D), a second layer forms on top of the initial one. e Microcolony size at the onset of second layer formation. In c and d, error bars are defined as s.e.m. (WT E. coli, red, N = 7; Δ₄pol purple, N = 5; Δ₄adh green, N = 5). Statistical analysis was performed using the unpaired t-test (***p-value < 0.001)