Abstract

Swimming bacteria such as E. coli are known to be able to explore their environment by performing a random walk. It is also know that they can follow chemical queues and drift up or down chemical concentration gradients. This movement in response to a chemical stimulus is known as chemotaxis. E. coli performs chemotaxis by increasing the time that they spend swimming up or down the gradient. This strategy is know to be efficient when the bacterium is swimming far away from any boundary, however most bacteria spend their life in confined environments and hydrodynamic interactions may decrease the effectiveness of this strategy. In this talk I will show that chemotaxis of E. coli is hindered when swimming near to a surface due to the effect of hydrodynamic interactions. First I will revisit the problem of diffusion of circle swimmer using an isotropic random walk with circular trajectories, interrupted by changes in direction. Chemotaxis is added by allowing the arc length of the trajectories to depend on a chemical concentration gradient and I will show that in the limit of shallow gradients, it is possible to obtain negative chemotaxis, that is drift away from an attractant.