From snowflake formation to growth of bacterial colonies .2. Cooperative formation of complex colonial patterns

In nature, bacterial colonies must often cope with hostile environmental conditions. To do so they have developed sophisticated cooperative behaviour and intricate communication capabilities, such as direct cell-cell physical interactions via extra-membrane polymers, collective production of extracellular 'wetting' fluid for movement on hard surfaces, long-range chemical signalling such as quorum sensing and chemotactic (bias of movement according to gradient of chemical agent) signalling, collective activation and deactivation of genes and even exchange of genetic material. Utilizing these capabilities, the bacterial colonies develop complex spatio-temporal patterns in response to adverse growth conditions. We present a wealth of beautiful patterns formed during colonial development of various bacterial strains and for different environmental conditions. Invoking ideas from pattern formation in non-living systems and using generic modelling we are able to reveal novel bacterial strategies which account for the salient features of the evolved patterns. Using the models, we demonstrate how bacterial communication lends to colonial self-organization that can only be achieved via cooperative behaviour of the cells. It can be viewed as the action of a singular feedback between the microscopic level (the individual cells) and the macroscopic level (the colony) in the determination of the emerging patterns.