Modelling finger-like pattern formation in a bacteria colony growing at an interface using dynamical self-consistent field theory*

Fascinating finger-like patterns are observed at the edge of Pseudomonas aeruginosa bacteria colonies that grow at the effectively two-dimensional interface between agar and glass. We study this pattern formation phenomenon by simulating a dynamical self-consistent field theory. The twitching bacteria are modelled as self-propelled rods pushing against the agar-glass adhesion force, represented as a bath of passive particles.  Fingers emerge in our simulation as regions of dense, nematically-aligned rods that move along the nematic director. We examine how a perturbation to an initially flat colony edge can evolve into a set of fingers. We investigate the relationship between the strength of the self-propulsive force and the finger speed. Introducing a random spatial variation in the agar-glass adhesion strength leads to finger shapes and finger motion similar to what is observed in experiments.