Abstract: How do growing bacterial colonies get their shape? While this process of morphogenesis is well-studied in 2D, many bacterial colonies inhabit 3D environments, such as gels and tissues in the body, or soils, sediments, and subsurface media. Here, we describe a morphological instability exhibited by dense colonies of non-motile bacteria growing in 3D. We elucidate this behavior using linear stability analysis and numerical simulations of a continuum active fluid model, which reveal that when the size of the growing colony far exceeds the nutrient penetration length, nutrient depletion drives a transition to roughening with a characteristic universal shape that can be compared with experiments.
Bio: Alejandro Martinez-Calvo is an HFSP (Human Frontier Science Program) fellow at the Princeton Center for Theoretical Science and the Department of Chemical and Biological Engineering at Princeton University. He obtained his Ph.D. in Fluid Dynamics under the supervision of Prof. Alejandro Sevilla at Universidad Carlos III de Madrid, supported by a FPU doctoral fellowship. His research is framed within the fields of soft/active matter, biological physics, and fluid dynamics. So far, he has studied systems involving small-scale interfacial flows, bulk and interfacial rheology, elasticity, and membrane dynamics. Currently, he is interested in several research areas within the context of biophysics and living matter, namely the dynamics of eukaryotic cells and tissues, and the physics of bacteria in complex habitats. He employs theory and accurate numerical methods to unravel the physics of these complex systems.