A multiphase approach to model bacterial biofilm

In this work, we use a modelling and experimental approach to study the self-organization of bacterial cells expanding on solid agar. Growing microbes form a biofilm by secreting extracellular polymeric substances (EPSs) that form an integral part of biofilm-like structures. In these structures, interaction among mechanical and physical forces results in different morphological patterns such as concentric rings, dendrites, Eden like structures. Surfactant molecules that lower the surface tension of the colony are secreted by these growing cells. Lowering the surface tension helps spreading of bacteria on solid surfaces. The difference in the surface concentration of surfactant molecules causes the Marangoni effect that facilitates spreading.

In this work, we study the effect of bacterial surfactant secretion, the diffusional flux of nutrients, substrate thickness and wettability on colony growth and shape within the framework of a hydrodynamic thin film model. Our framework accounts interplay among mechanical stress from bacterial migration, growth, surface stress and Marangoni effects. Our mathematical model is able to explain front instability in bacterial colony patterns and various experimental observations of microbial colony patterns in literature.