Mechanically-driven spreading of bacterial populations

•The expansion of bacterial colonies in the presence of exclusion process was investigated.•The degenerate Fisher-KPP equation was extended by incorporating the cell size into the model.•The traveling wave solutions of this equation were studied both analytically and numerically.•The dependence on packing fraction of bacterial colony expansion speed was found.

The effect of mechanical interactions between cells in the spreading of bacterial populations was investigated in one-dimensional space. A continuum-mechanics approach, comprising cell migration, proliferation, and exclusion processes, was employed to elucidate the dynamics. The consequent nonlinear reaction-diffusion-like equation describes the constitution dynamics of a bacterial population. In this model, bacterial cells were treated as rod-like particles that interact with each other through hard-core repulsion, which introduces the exclusion effect that causes bacterial populations to migrate quickly at high density. The propagation of bacterial density as a traveling wave front over extended times was also analyzed. The analytical and numerical solutions revealed that the front speed was enhanced by the exclusion process, which depended upon the cell-packing fraction. Finally, we qualitatively compared our theoretical results with experimental evidence.