CHEMOMODULATION OF CELLULAR-MOVEMENT, COLLECTIVE FORMATION OF VORTICES BY SWARMING BACTERIA, AND COLONIAL DEVELOPMENT

Bacterial colonies have developed sophisticated modes of cooperative b ehavior which enable them to respond to adverse growth conditions. It has been shown that such behavior can be manifested in formation of co mplex colonial patterns. Certain Bacillus species exhibit collective m igration, ''turbulent like'' flow and emergence of whirlpools during c olonial development. Here we present experimental observations of coll ective behavior and a generic model to explain such behavior. The mode l incorporates self-propelled and interacting ''particles'' (swarmers) . We show that velocity interaction between the particles can lead to a synchronized movement. To explain vortices formation, we propose a p lausible mechanism involving a special chemotactic response (rotationa l chemotaxis) which is based on speed modulations according to the con centration of a chemoattractant. This mechanism differs from that exhi bited by swimming bacteria. We show that the chemomodulation of swarme rs' speed together with the velocity interactions impose a torque on t he collective motion and can lead to formation of vortices. The inclus ion of both attractive and repulsive rotational chemotaxis in the mode l captures the salient features of the observed growth patterns.