Figure 2.

Self-organized swarm pattern generated by chemotaxing E. coli. Shown is the negative image of a bacterial culture in which growth was initiated at the center of a semisolid medium of defined composition. The pattern was formed over a period of three days as the cells swarmed outward from the center, migrating in response to self-generated gradients of chemical attractants. Dark areas indicate regions of high cell density (Budrene & Berg 1995).