(111i) Morphogenesis of Growing Bacterial Colonies in Polymeric Environments

Many bacteria live in polymeric environments, such as mucus in the body, exopolymers in the ocean, and cell-secreted extracellular polymeric substances (EPS) that encapsulate biofilms. However, most studies of bacteria focus on cells in polymer-free fluids. How do interactions with polymers influence the behavior of growing bacterial communities? To address this question, we experimentally probe the growth of non-motile Escherichia coli in solutions of inert polymers. We find that, when the polymer is sufficiently concentrated, the cells grow in striking "cable-like" morphologies—in stark contrast to the compact morphologies that arise in the conventionally-studied polymer-free case. Experiments and agent-based simulations suggest that these unusual community morphologies arise due to a polymer-induced entropic attraction between pairs of cells. These results suggest a pivotal role of polymers in regulating microbe-host interactions, by promoting bacterial exposure to external biochemical groups that protect the host against pathogens. More broadly, this work helps to uncover quantitative principles governing the morphogenesis of diverse forms of growing active matter in polymeric environments.