Run-and-Tumble Bacterial Chemotaxis in Confinement*

Most bacteria live in complex porous materials such as tissues or soil, yet their motion and chemotaxis in confinement are still not well understood.

We present a run-and-tumble model for bacterial motion model coupled to the chemical gradient while the entire colony is inside a circular confinement. For the tumble timing, we consider a smooth transition from the `run' to `tumble' motion.The tumble angle follows a bimodal von Mises distrbution which has a one-sided mean and a reciprocal measure of dispersion. We present simulations of the collective chemotactic behavior in confinement when swimmers are either fully motile or  random mixture of motile and immotile. Finally, we will discuss the states observed for various parameters, and the phase separation of bacteria in confinement.