We present results of experiments on the dynamics of Dictyostelium discoideumin a novel set-up which constraints cell motion to a plane. After aggregation,the amoebae collect into round ''pancake" structures in which the cells rotatearound the center of the pancake. This vortex state persists for many hours andwe have explicitly verified that the motion is not due to rotating waves ofcAMP. To provide an alternative mechanism for the self-organization of theDictyostelium cells, we have developed a new model of the dynamics ofself-propelled deformable objects. In this model, we show that cohesive energybetween the cells, together with a coupling between the self-generatedpropulsive force and the cell's configuration produces a self-organized vortexstate. The angular velocity profiles of the experiment and of the model arequalitatively similar. The mechanism for self-organization reported here canpossibly explain similar vortex states in other biological systems.
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