Growth-induced mechanical interactions shape microbial colony expansion: a model of self-replicating living fluids

Microbial colonies are soft living materials whose growth and architecture are shaped by cellular growth and mechanical interactions. Understanding how these colonies expand and deform offers a window into understanding the physics of active soft matter, and the adaptation of dense microbial populations to surface growth. In this work, we investigate the radial expansion and height evolution of non-motile Saccharomyces cerevisiae colonies experimentally and develop a continuum-based model that couples cellular growth and division, nutrient diffusion and uptake, colony rheology, and thin-film mechanics to describe the spatiotemporal evolution of colony height and local glucose concentration in one- and two-dimensional landscapes. This framework further reveals how rheological and metabolic parameters jointly control colony morphology and spreading dynamics, linking mechanical and biochemical regulation within growing cellular assemblies. Together, these results highlight S. cerevisiae colonies as a model system for studying how mechanical interactions within dense cellular systems and nutrient limitation jointly regulate biofilm-like growth and shape the evolutionary dynamics of microbial populations.