On Growth and Form of Range Expansions at Liquid Interfaces

Range expansions coupled with fluid flows are of great importance in understanding the organization and competition of microorganism populations in liquid environments. However, combining growth dynamics of an expanding assembly of cells with hydrodynamics leads to challenging problems, involving the coupling of nonlinear dynamics, stochasticity and transport. We have created an extremely viscous medium that allows us to grow cells on a controlled liquid interface over macroscopic scales. In this talk, I will present laboratory experiments, combined with numerical modelling, focused on the collective dynamics of genetically labelled microorganisms undergoing division and competition in the presence of a flow. I will show that an expanding population of microbes can itself generate a flow, leading to an accelerated propagation and fragmentation of the initial colony. Finally, I will show the mechanism at the origin of this metabolically generated flow and how it affects the growth and morphology of these microbial populations.