Hydrodynamics of bacterial colonies

Understanding the growth and dynamics of bacterial colonies is a fascinating problem, which requires combining ideas from biology, physics and applied mathematics. We briefly review the recent experimental and theoretical literature relevant to this question and describe a hydrodynamic model (Lega and Passot 2003 Phys. Rev. E 67 031906, 2004 Chaos 14 562-70), which captures macroscopic motions within bacterial colonies, as well as the macroscopic dynamics of colony boundaries. The model generalizes classical reaction-diffusion systems and is able to qualitatively reproduce a variety of colony shapes observed in experiments. We conclude by listing open questions about the stability of interfaces as modelled by reaction-diffusion equations with nonlinear diffusion and the coupling between reaction-diffusion equations and a hydrodynamic field.