Hydrodynamic and Interfacial Principles of Swarming Biofilms

Self-assembly refers to the process by which colloidal particles or other discrete components, such as viruses or bacteria, spontaneously organize into ordered, macroscopic structures. Essential is that the colloidal building blocks undergo this restructuring process either through direct interactions, such as interparticle forces, or indirectly using a template or an external field. Recent advances have highlighted the similarity between the self-organization in bacterial systems and those observed in certain colloidal systems, when the latter mimic the properties of the bacteria as far as shape and size are concerned. Too often in the biological literature, intricate genetic mechanisms are proposed to explain the self-assembly, whereas simple physicochemical or hydrodynamic mechanisms are not considered. Bacterial swarming, the rapid spreading of a colony over surfaces, is a process triggered by a depletion of available food sources. Hence, it is a natural reaction to an unfavorable state and a potential survival strategy used by biological organisms. Although the active nature and the motility of bacteria have long been considered to be the main contributors, the importance of interfacial effects in the efficiency as well as the pattern formation have recently been suggested. Other mechanisms, such as hydrodynamics and viscoelasticity effects, have not yet been studied, whereas this may be key in understanding the phenomena of bacterial cell transport. The knowledge in this efficient structuring by self-assembly can be used to arrest the spreading of unwanted bacterial species or vice versa to create optimal growth and bioavailability of bacteria. This thesis aims at a rational approach to study the similarity and differences of self-assembly in active and passive systems, and to understand the physicochemical mechanisms that drive self-assembly in bacterial systems.nrpages: 182status: publishe