Morphogenesis of bacterial colonies in liquid crystalline environments

Many bacteria live in liquid crystalline (LC) environments, from mucus to biofilms. We explore how such anisotropic, viscoelastic fluids can shape a fundamental feature of bacterial life - how they proliferate in space in multicellular colonies. Using experiments, we find that when grown in a LC, cells form large single-cell width chains that at sufficiently long lengths undergo a mechanical buckling instability. We then argue, using a continuum mechanical theory, that these dynamics emerge because cells are kept in alignment by the medium's elasticity, and that growth-induced stresses along the bacterial chain's length eventually promote its buckling. The critical buckling length is found to depend primarily upon an Ericksen number, which compares growth-induced viscous stresses to elastic stresses, and to a dimensionless LC anchoring strength. Our work thus reveals how a liquid crystalline environment sculpts proliferating bacterial colonies, with implications for how they interact with hosts and with the natural environment, and uncovers quantitative principles governing colony morphogenesis in complex fluids. This is joint work in collaboration with Sebastian Gonzalez La Corte (Princeton), Thomas Chandler (UNC), Ned Wingreen (Princeton), and Sujit Datta (Caltech).