Modeling microbial colonies as living materials

Microbial colonies and biofilms are central to human health and technological applications, yet quantitative modeling of their surface colonization dynamics remains underdeveloped. For non-motile microbes, colony and biofilm expansion occurs through growth, division, and collective cell motion, influenced by nutrient availability and the rheological properties of these dense cellular populations. Here, we model their spatiotemporal dynamics by treating microbial colonies as living materials and examine how colony rheology, surface tension, and substrate friction shape expansion dynamics. Using a thin-film fluid mechanics approach, we derive equations for colony height dynamics that incorporate the rheological properties of these living materials. Our analysis reveals traveling wave solutions that characterize the steady advancement of the colony front. These waves emerge from the interplay between growth dynamics and internal mechanical stresses, shedding light on the mechanisms driving microbial expansion on surfaces.