Fig. S8.

Probability to observe colony surfing in a bare polystyrene Petri dish at 15° tilt, closed, and with a water reservoir at the bottom, as a function of the initial deposited volume. The surfactin-producing strain SSB 1071 starts to slide at much smaller volumes ($V_i^{\text{crit}}=4\mathrm{\mu }\text{L}$) compared with water and the surfactin-deficient 168 strain. The experimental protocol closely follows that of the experiments on gel. The bacterial suspension is prepared using the same protocol (Materials and Methods). Drops of different volume at an initial optical density of $\text{OD}=\mathrm{\hspace{0.17em}0.27}$ are deposited in an inclined clean polystyrene Petri dish placed inside a climate chamber (T = 30 °C, RH = 70%); (Inset) 10 mL of distilled water is added at the bottom of the dish as a source of humidity. Finally, the Petri dish cover lid is put in place and the chamber is closed. Four drops were measured for each condition.