Expanding Bacterial Active Matter – X-BACAMAT

Active matter, a term coined by physicists to describe a large number of agents consuming energy to move or exert mechanical forces, has become a major field of research in biological physics. A colony of motile bacteria is a good example of growing active matter: each cell can grow and divide, and it can move around thanks to its flagella. Growing active matter with microswimmers raises specific questions: What is the contribution of growth in long-range ordering patterns that are typically obtained in dense bacterial suspension? What is the influence of swimming modes, namely the pusher and puller mode used to describe two types of microswimmers, in tetratic and nematic alignement? How do physical effects translate across scales? This project proposes to use the bacterium Pseudomonas aeruginosa as an experimental model system to answer these questions. I will use a suite of imaging devices and methods across all scales, from single-cell to the whole colony, and with transmission, reflection, and fluorescence imaging. I will also use genetic engineering to modulate motility as an experimental variable. The tasks presented in the project are ordered in increasing length and time scales: from the hydrodynamics of P. aeruginosa single cells to 2D and 3D orderings, the physics of spreading of active fluid, the dynamics of layered organization, the dynamics of binary mixtures of cells with different motility properties, and, for much longer time scales, evolutionary dynamics of motility.