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.