  We study the formation of spot patterns seen in a variety of bacterial
species when the bacteria are subjected to oxidative stress due to hazardous
byproducts of respiration. Our approach consists of coupling the cell density
field to a chemoattractant concentration as well as to nutrient and waste
fields. The latter serves as a triggering field for emission of
chemoattractant. Important elements in the proposed model include the
propagation of a front of motile bacteria radially outward form 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 explained as being due the variation of the
details of the initiation of the chemoattractant emission as well as the
transition to a non-motile phase.
