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Center for Nonlinear Studies |
Periodic reversal of direction allows myxobacteria to swarm
Many bacteria can rapidly traverse surfaces from which they are extracting nutrient for growth. They generate flat, spreading colonies, called swarms because they resemble swarms of insects. We seek to understand how members of a dense swarm population track their neighbors while interfering minimally with the motion of others'. For this purpose, we are investigating swarms of the myxobacterium, Myxococcus xanthus. Individual M. xanthus cells are elongated; they always move in the direction of their long axis. Curiously, they reverse their gliding direction at nearly constant intervals. We have constructed a detailed cell- and behavior-based computational model of M. xanthus swarming, and are able to show that reversals of gliding direction increase the outflow of cells across the edge of the swarm, and that reversals are essential for swarming. We also find that the reversal period predicted to maximize the cell flux is the same (within the errors of measurement) as the period observed in experiments with normal M. xanthus cells. This coincidence suggests that the circuit regulating reversals evolved to its current state under selection for growth with swarming.