Fig. 4.
Probability of cell detachment from the surface as a function of obstacle density. a Probability of detachment from the surface as a function of the obstacle density ρ for E. coli cells swimming through a circular area of radius R = 25 μm. This probability is calculated by considering all cells’ trajectories that enter the circular area through its perimeter (i.e. that are entrapped at the surface) and leave it either through its perimeter (i.e. still entrapped at the surface, ) or by moving out of plane (N⊥). The samples are analogous to those in Fig. 1 (Methods) with sparse 10-μm polystyrene particles as spacers. Each value is obtained by averaging over at least five independent experiments. The shaded area around the average values represents one standard deviation. In each independent experiment, at least 70 different trajectories were used to determine the probability of detachment from the surface for every value of ρ. b–d Exemplary trajectories showing E. coli cells that b remain entrapped at the surface in the absence of obstacles, c detach from the surface after a forward-scattering event, and d remain entrapped at the surface after a tumble-collision. The white triangles on the trajectories represent the direction of motion when entering and leaving the circular area either through the perimeter (i.e. still entrapped at the surface) or by moving out of plane, while the colour code of the trajectories represents the cells’ instantaneous velocity v normalised to its maximum value. The black scale bar in b corresponds to 10 μm