Aggregation Patterns in Stressed Bacteria

We study the formation of spot patterns seen in bacterial colonies when the bacteria are subjected to oxidative stress due to hazardous by-products of respiration. The cell density is coupled to a chemoattractant concentration as well as to nutrient and waste fields. The model combines the propagation of a front of motile bacterial radially outward from an initial site, a Turing instability of the uniformly dense state, and a reduction of motility for cells sufficiently far behind the front. The wide variety of patterns seen in the experiments is reproduced by the model by varying the details of the initiation of the chemoattractant emission as well as the transition to a nonmotile phase.