Periodic Pattern Formation of Bacterial Colonies

Abstract

We have experimentally investigated pattern formation of colonies of bacterial species Proteus mirabilis , which is famous for forming concentric-ring-like colonies. The colony grows cyclically with the interface repeating an advance and a stop alternately on a surface of a solid agar medium. We distinguish three phases (initial lag phase, the following migration and consolidation phases that appear alternately) for the colony growth. When we cut a colony just behind a migrating front shortly after the migration started, the migration ended earlier and the following consolidation lasted longer. However, the following cycles were not influenced by the cut, i.e., the phases of the migration and consolidation were not affected. Global chemical signals governing the colony formation from the center were not found to exist. We also quantitatively checked phase entrainment by letting two colonies collide with each other and found that it does not take place in macroscopic scales. All these experimental results suggest that the most important factor for the migration is the cell population density.