Anomalous diffusion of E. coli under microfluidic confinement and chemical gradient

We report a two-layer microfluidic device to study the combined effect of confinement and chemical gradient on the motility of wild type E. coli. We track individual E. coli in 50μm and 10μm wide channels, with a channel height of 2.5μm, to generate quasi-2D conditions. We find that contrary to expectations, bacterial trajectories are super-diffusive even in absence of a chemical (glucose) gradient. The superdiffusive behaviour becomes more pronounced on introduction of a chemical gradient or on strengthening the lateral confinement. Runlength distributions for weak confinement in absence of chemical gradients follow an exponential distribution. Both confinement and chemoattraction induce deviations from this behaviour, with the runlength distributions approaching a power-law form under these conditions. Both confinement and chemoattraction suppress large angle tumbles as well. Our results suggest that wild-type E. coli modulates both its runs and tumbles in a similar manner under physical confinement and chemical gradient.