Follow my lead: Bacterial trail in entangled polymer solutions

In a medium of slow relaxation, such as viscoelastic fluids, a moving particle can leave behind transient heterogeneities in its trail that can affect another particle’s trajectory. These remote heterogeneity-induced interactions may matter to motile bacteria in their complex biological environment. Our quasi-2D model system—motile B. subtilis in an entangled polymer solution—allows us to characterize the time-varying heterogeneities, bacterial trajectories, and the trail-bacteria interactions. Specifically, in the polymeric environment, a bacterium can chase the leading bacterium over distances of several hundred microns, following the identical trajectory. Combining systematic investigation, varying polymer types and concentrations, and statistical analysis, we discuss the physics behind the trail-bacteria interactions. Our study demonstrates that active particles sharing no chemical cues can interact remotely and enhance bacterial diffusion.