Mechanically driven growth of quasi-two dimensional microbial colonies

TL;DR

This paper models non-motile bacterial colonies growing on solid surfaces, revealing how mechanical interactions influence growth dynamics, shape, and transitions, which are not explained by traditional models.

Contribution

It introduces a mechanical interaction-based model for bacterial colony growth, highlighting effects on velocity, shape, and colony morphology transitions.

Findings

Velocity depends on bacterial elastic modulus and surface stickiness.

Incompressible 2D colonies cannot grow linearly in time.

Mechanical interactions explain shape transitions from circular to branching.

Abstract

We study colonies of non-motile, rod-shaped bacteria growing on solid substrates. In our model, bacteria interact purely mechanically, by pushing each other away as they grow, and consume a diffusing nutrient. We show that mechanical interactions control the velocity and shape of the advancing front, which leads to features that cannot be captured by established Fisher-Kolmogorov models. In particular, we find that the velocity depends on the elastic modulus of bacteria or their stickiness to the surface. Interestingly, we predict that the radius of an incompressible, strictly two-dimensional colony cannot grow linearly in time. Importantly, mechanical interactions can also account for the nonequilibrium transition between circular and branching colonies, often observed in the lab.