Interactions of E. coli with cylindrical micro-pillars of different geometric modifications

Understanding the behavior of bacteria at the proximity of different surfaces is of great importance and interest. Despite recent exciting progress in geometric control of bacterial behavior around surfaces, a detailed comparison on the interaction of bacteria with cylindrical surfaces of different geometric modifications is still missing. Here, we investigated how bacteria interacted with cylindrical micro-pillars and modified cylindrical micro-pillars with sprocket, gear, and flower-like wall surface features. Using phase-contrast microscopy, we examined the motion of bacteria around the micro-pillars, and observed different responses of bacteria to each geometric modification. In addition, we extracted the trajectories of the bacteria and characterized several parameters (instantaneous velocity v, change of direction δ, approaching angle ϕ) to quantitatively compare the effects of the geometric modifications on the micro-pillars. We found that sharp spikes showed the largest effect, compared to smooth surface, convex and concave ripples. Lastly, we carried out numerical simulations, which explained the experimental observations and showed that the observed effects were due to the geometric modifications.