Phase behavior of bacterial binary mixtures

• Applicant: Dr. Remy Colin
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448615934

In bacterial populations, swimming motility drives the emergence of complex self-organized dynamics. Coupled to biochemical regulations, these collective effects govern the organization of bacterial communities, with examples ranging from motility-driven surface colonization to biofilm formation. Therefore, not only are bacterial populations powerful model systems for studying the physics of active matter, but the lessons learned also find direct applications to understanding their biology. In natural communities, multiple species usually co-exist, some motile and others not. Although the role of biochemical interactions between species in shaping the community is increasingly investigated, the physical behavior of heterogeneous bacterial mixtures remains largely unexplored. Previous experiments and theory have indeed mostly focused on homogeneous populations of swimmers. This research proposal aims at starting filling this gap. We study experimentally the physical behavior of mixtures of motile and non-motile bacteria, both derived from the model organism E. coli to eliminate complex cross-species biochemical interactions. Preliminary results show density pattern formation in a wide range of conditions, with properties that might indicate a phase separation of the mixture. The proposed work aims at understanding the physics at play and the consequences for the structuration of multispecies bacterial communities, both at rest and under constraint. We will build the full phase diagram of the binary mixture, varying potential control parameters (cell size, swimming speed, suspension confinement…) to decipher the physical mechanism(s) driving pattern formation. We will then investigate its effects on bacterial self- and co-aggregation, to better understand the physics of multispecies biofilm formation. Finally we will measure how the mixture responds to chemical and mechanical constraints, to better understand both its physics and biology. To these aims, we will combine the genetic tractability of E. coli, micro-fabricated, and thus well-controlled, experimental devices and image analysis tools developed in our previous research on bacterial motility.

• DFG Programme: Research Grants