Cellular Sensing Governs the Stability of Chemotactic Fronts

In contexts ranging from embryonic development to bacterial ecology, cell populations migrate chemotactically along self-generated chemical gradients, often forming a propagating front. Here, we theoretically show that the stability of such chemotactic fronts to morphological perturbations is determined by limitations in the ability of individual cells to sense and thereby respond to the chemical gradient. Specifically, cells at bulging parts of a front are exposed to a smaller gradient, which slows them down and promotes stability, but they also respond more strongly to the gradient, which speeds them up and promotes instability. We predict that this competition leads to chemotactic fingering when sensing is limited at too low chemical concentrations. Guided by this finding and by experimental data on E. coli chemotaxis, we suggest that the cells' sensory machinery might have evolved to avoid these limitations and ensure stable front propagation. Finally, as sensing of any stimuli is necessarily limited in living and active matter in general, the principle of sensing-induced stability may operate in other types of directed migration such as durotaxis, electrotaxis, and phototaxis.

Automated summary

This article theoretically demonstrates the limitations in stability of chemotactic fronts to morphological perturbations caused by the ability of individual cells to sense and respond to chemical gradients. The competition between cells at bulging parts of a front, where they are exposed to a smaller gradient but respond more strongly to it, determines whether the front is stable or not. The study suggests that the sensory machinery of cells might have evolved to avoid these limitations and ensure stable front propagation, and this principle may also apply to other types of directed migration.