FORMATION OF COMPLEX BACTERIAL COLONIES VIA SELF-GENERATED VORTICES

Depending on the environmental conditions bacterial colonies growing o n agar surfaces can exhibit complex colony formation and various types of collective motion. Experimental results are presented concerning t he hydrodynamics (vortices, migration of bacteria in clusters) and col ony formation of a morphotype of Bacillus subtilis. Some of these feat ures are not specific to this morphotype but also have been observed i n several other bacterial strains, suggesting the presence of universa l effects. A simple model of self-propelled particles is proposed, whi ch is capable of describing the hydrodynamics on the intermediate leve l, including the experimentally observed rotating disks of bacteria. T he colony formation is captured by a complex generic model taking into account nutrient diffusion, reproduction, and sporulation of bacteria , extracellular slime deposition, chemoregulation, and inhomogeneous p opulation. Our model also sheds Light on some possible biological bene fits of this ''multicellular behavior.''