Self-organized Vortex State in Two-DimensionalDictyosteliumDynamics

We present results of experiments on the dynamics of Dictyostelium discoideum in a novel setup which constrains cell motion to a plane. After aggregation, the amoebae collect into round ``pancake'' structures in which the cells rotate around the center of the pancake. To provide a mechanism for the self-organization of the Dictyostelium cells, we have developed a new model of the dynamics of self-propelled deformable objects. In this model, we show that cohesive energy between the cells, together with a coupling between the self-generated propulsive force and the cell's configuration, produces a self-organized vortex state. The mechanism for self-organization reported here can possibly explain similar vortex states in other biological systems.