Severine ATIS, From growing cells to activated particles: How to self-organize within flows

Biological systems can self-organize in complex structures, able to evolve and adapt to widely varying environmental conditions. Despite the importance of fluid flow for transporting and organizing populations, few laboratory systems exist to systematically investigate the impact of advection on their spatial evolutionary dynamics. In the first part of this talk, I will discuss how we can address this problem by studying the morphology and genetic spatial structure of microbial colonies growing on the surface of a viscous substrate. When grown on a liquid, I will show that S. cerevisiae (baker’s yeast) can behave like “active matter” and collectively generate a fluid flow many times larger than the unperturbed colony expansion speed, which in turn can produce mechanical stresses and preferential growth. Combining laboratory experiments with numerical modeling, I will demonstrate that the coupling between metabolic activity and hydrodynamic flows can generate positive feedbacks and lead to the complete fragmentation of the initial colony or drive the formation of growing microbial jets. In the second part, I will present an artificial system composed of thousands of activated magnetic particles submerged in a fluid. When rapidly rotated by an external field, the competition between magnetic and hydrodynamic interactions between the particles generates collective states with complex dynamics in 3-dimensions. I will show that these interactions can be directly tuned with the geometry and amplitude of the hydrodynamic field created around the particles by controlling the magnetic field rotation properties.