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Dale Kaiser
Stanford University

Pattern Formation in Myxobacteria

Myxobacteria are single cells that organize several multicellular patterns. To gather food for growth, cells swarm outward at constant rate for weeks. When the swarm exhausts its food supply, the cells stop spreading outward and begin moving inward. Finally they form fruiting bodies of 100,000 cells whose shape is species specific. Spores differentiate within the fruiting body. The genome of Myxococcus xanthus has been sequenced; its genes can readily be manipulated, and individual cells can be tracked.

Early in the process of building fruiting bodies, waves of high cell density sweep across the swarm. Small traffic jams arise within a field of waves from cells that converge on the same focus from several directions. Such foci enlarge as cells stream over and around them in circular orbits. The streams constitute a set of concentric spherical shells, like the skins of an onion. Slow dissolution of the traffic jam at the center of the onion hollows it. The resulting spherical aggregate is capable of fusing with others of its kind until the aggregate reaches fruiting body size (1). Both the waves and aggregation depend on a morphogen, a 17 kDa, surface-bound protein called the C-signal. Several mathematical models of cell movement and signaling in the traveling waves has been developed that agree with the recorded trajectories of single cells (2,3). Moreover, the model has been extended to explain the position and form of the aggregates (4). The model depends on signaling by cell-cell contact, C-signal is not diffusible.

(1) Kaiser D and Welch R (2004) Dynamics of fruiting body morphogenesis. J Bacteriol.186: 919-27.

(2) Welch R and Kaiser, D. (2001) Cell behavior in traveling wave patterns of myxobacteria. Proc. Natl. Acad. Sci. USA98: 14907-14912.

(3) Igoshin O, Welch R, Kaiser D, and Oster G (2004) Waves and aggregation patterns in Myxobacteria. Proc. Natl. Acad. Sci. USA101 15760-15765.

(4) Sozinova, O., Jang, Y., Kaiser, D., and Alber, M.S. (2005) Three-dimensional model of myxobacterial aggregation by contact-mediated interaction. Proc Natl Acad Sci U S A102: 11308-11312.

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