Accidental and Regulated Cell Death in Yeast Colony Biofilms

The yeast species Saccharomyces cerevisiae is one of the most intensively studied organisms on the planet due to it being an excellent eukaryotic model organism in molecular and cell biology. In this work, we investigate the growth and morphology of yeast colony biofilms, where proliferating yeast cells reside within a self-produced extracellular matrix. This research area has garnered significant scientific interest due to its applicability in the biological and biomedical sectors. A central feature of yeast colony biofilm expansion is cellular demise, which is onset by one of two independent mechanisms: either accidental cell death (ACD) or regulated cell death (RCD). In this article, we generalise a continuum model for the nutrient-limited growth of a yeast colony biofilm to include the effects of ACD and RCD. This new model involves a system of four coupled nonlinear reaction-diffusion equations for the yeast-cell density, the nutrient concentration, and two species of dead cells. Numerical solutions of the spatially one and two-dimensional governing equations reveal the impact that ACD and RCD have on expansion speed, morphology and cell distribution within the colony biofilm. Our results are in good qualitative agreement with our own experiments.