Abstract
How motile bacteria move near a surface is a problem of fundamental biophysical interest and is key to the emergence of several phenomena of biological, ecological and medical relevance, including biofilm formation. Solid boundaries can strongly influence a cell’s propulsion mechanism, thus leading many flagellated bacteria to describe long circular trajectories stably entrapped by the surface. Experimental studies on near-surface bacterial motility have, however, neglected the fact that real environments have typical microstructures varying on the scale of the cells’ motion. Here, we show that micro-obstacles influence the propagation of peritrichously flagellated bacteria on a flat surface in a non-monotonic way. Instead of hindering it, an optimal, relatively low obstacle density can significantly enhance cells’ propagation on surfaces due to individual forward-scattering events. This finding provides insight on the emerging dynamics of chiral active matter in complex environments and inspires possible routes to control microbial ecology in natural habitats.
Highlights
How motile bacteria move near a surface is a problem of fundamental biophysical interest and is key to the emergence of several phenomena of biological, ecological and medical relevance, including biofilm formation
To identify how the spatial heterogeneity on flat surfaces influences the propagation of bacteria, we recorded trajectories of motile E. coli cells swimming near a glass surface in a quasi-2D geometry with different densities ρ of fixed obstacles in the range 0% ≤ ρ ≤ 12% (Methods)
E. coli bacteria are peritrichously flagellated prokaryotic cells that swim through an alternation of run and tumble events[9]
Summary
How motile bacteria move near a surface is a problem of fundamental biophysical interest and is key to the emergence of several phenomena of biological, ecological and medical relevance, including biofilm formation. An optimal, relatively low obstacle density can significantly enhance cells’ propagation on surfaces due to individual forward-scattering events This finding provides insight on the emerging dynamics of chiral active matter in complex environments and inspires possible routes to control microbial ecology in natural habitats. The interaction with the obstacles can, rectify the cells’ near-surface motion chirality over distances orders-of-magnitude longer than the typical cell size This behaviour is fundamentally different from that of non-chiral active colloids cruising through random obstacles with a fixed motion strategy, which instead get more localised for increasing obstacle densities[31,40,41]. Verify numerically, a microscopic understanding of the transition between enhanced surface propagation and localisation by identifying two types of cell–obstacle interactions, namely forwardscattering events and head-on tumble-collisions
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