In a previous post on the Keller-Segel model I raised some questions concerning the applicability of the model to the aggregation of Dictyostelium discoideum. A coherent picture of the early stages of this process is presented in a review paper of Ben-Jacob, Cohen and Levine entitled ‘Cooperative self-organization of microorganisms’ (Adv. Phys. 49, 395-554), which I found on the web page of Levine. According to the account given there there is a first phase involving spiral waves and chemotaxis only starts to play a role after that. The tips of the spiral waves define the centres of the aggregation process. See Fig. 31 of the paper. There are also interesting comments on the role of adhesion later in the process of aggregation where streams are formed. All of this is backed up by extensive references. I was interested to see that several of the topics discussed in this blog are mentioned in the paper of Ben-Jacob et. al. (Liesegang rings, chemotaxis, quorum sensing, dynamics of actin polymerization, bacterial motion, Keller-Segel model, Dictyostelium). Thus there may be more unity in my apparently rather random musings than I had realized.
The paper of Ben-Jacob at. al. appears to be a rich repository of ideas about mathematics, physics, biology and their mutual interactions. It also contains many striking pictures of the patterns which microorganisms, in particular bacteria, can produce.