Growth Process of Disk- and Rod- Shaped Bacterial Colonies in 2D

Abstract

Bacterial colonies play an important role in the global ecosystem, but the mechanical interactions between bacteria are not always well understood. In this thesis, we investigated the role of the aspect ratio (e.g. disk- and rod shaped bacteria) and the ratio between diffusion and duplication rate on the size and shape of a bacterial colony. We simulated growing bacterial colonies of particles with different aspect ratios in 2D using Brownian dynamics. The simulated colonies are analysed by looking at their mean radius, shape and the nematic order parameter. We find that for all the simulations the mean radius grows exponentially in time. For the rod-shaped bacterial colonies we find that the system starts in an elliptical nematic state that converges in time slowly to a circular isotropic state, due to outward radial pressure and the creation of disorder. The disk-shaped bacterial colonies with a fixed duplication direction start as well with an elliptical shape that converges to a circular shape. For a growing disk-shaped bacterial colony with a random duplication direction, we always find a circular shape. Moreover, we find that a higher diffusion rate leads to a higher mean radius of a bacterial colony on a short timescale but on a longer timescale the diffusion rate does not affect the mean radius due to the dominancy of the duplication rate. In future research it would be interesting to look at polydisperse colonies consisting of bacteria with different aspect ratios.