A model aided understanding of spot pattern formation in chemotactic E. coli colonies

Colonies of mutant E. coli strains, when inoculated in the centre of a plate, form highly symmetric, stable spot patterns. These spot patterns are only observed in chemotactic E. coli strains, i.e. strains that bias their motion so that cell populations move up gradients of a chemical in the cells’ local environment. It is an important question whether these patterns are due to genetic control or self-organization. Here we present a macroscopic continuum model of E. coli pattern formation that incorporates cell diffusion, chemotaxis, population growth and conversion to an inactive state. This model satisfactorily reproduces the observed spot patterns, supporting the view that these patterns are indeed a result of self-organization, and allows us to infer plausible minimal mechanisms that generate the observed patterns.