Cooperative strategies in formation of complex bacterial patterns

In nature, bacterial colonies often must cope with hostile environmental conditions. To do so they have developed sophisticated cooperative behavior and intricate communication channels on all levels. The result is that a profusion of complex patterns are formed during growth of various bacterial strains and for different environmental conditions. Some qualitative features of the complex morphologies may be accounted for by invoking ideas from pattern formation in non-living systems together with a simplified model of chemotactic ''feedback''. We present a non-local communicating walkers model to study the effect of local bacterium-bacterium interaction and communication via chemotaxis signaling. The model is an hybridization of the continuous approach (to handle chemicals' diffusion) and the atomistic approach (each ''atom'' or ''walker'' represents 10(4)-10(5) bacteria). Using the model we demonstrate how communication enables the colony to develop complex patterns in response to adverse growth conditions. Efficient response of the colony requires self-organization on all levels, which can be achieved only via cooperative behavior of the bacteria. It can be viewed as the action of an interplay between the micro-level (the individual bacterium) and the macro-level (the colony) in the determination of the emerging pattern. We show that seemingly unrelated patterns can result from the employment of the same generic strategies.