Chemotactic smoothing of bacterial populations

How do bacterial populations regulate morphology? Previous studies have identified several key factors that play a role in population morphogenesis, such as differential growth, intercellular mechanics, substrate interactions, and osmotic stresses. Here, we describe a previously undocumented mechanism by which bacterial populations regulate their morphology: via self-generated chemotaxis, biased motion in response to a self-generated nutrient gradient. Using experiments on 3D-printed bacterial populations, we demonstrate that this mechanism causes perturbations in population morphology to self-smooth, and characterize its dependence on cellular motility and initial population morphology. Further, by combining continuum-scale simulations with a linear stability analysis, we identify two distinct modes in which chemotaxis smooths a population: through differential cellular motility in response to either morphology-dependent nutrient availability or morphology-dependent nutrient sensing. Our analysis quantifies the rate at which these modes smooth perturbations in general, providing a framework by which chemotactic smoothing can be predicted and controlled.