3-D Numerical Simulations of Biofilm Dynamics with Quorum Sensing in a Flow Cell

Biofilms are microorganisms, where bacteria are embedded in networks formed by bacteria-produced expopolysacharrides, also known as extracellular polymeric substances EPS. Bacteria in biofilms communicate and cooperate with each other by sensing the density of signalling molecules that bacteria excrete. This phenomenon is known as quorum sensing QS In this paper, we develop a hydrodynamic model for biofilms to include quorum sensing in biofilm dynamics, extending previous models for biofilms. In the new model, we classify bacteria into down-regulated and up-regulated quorum sensing cells, as well as non quorum sensing cells based on their quorum sensing ability. We then develop a numerical simulation tool for studying biofilms under quorum sensing in an aqueous environment by solving the hydrodynamic model in full 3D in space and time. Our numerical results show that this model captures key features of quorum sensing regulation that are responsible for the development of heterogeneous biofilm structures. For instance, numerical simulations with the model show that quorum sensing is beneficial for the biofilm development in a long run by building a robust EPS population to protect the biofilm, but maybe of little benefit in some short time frame because it slows down the development of biofilm colonies. In addition, numerical simulations demonstrate that quorum sensing induction in biofilms is sensitive to the hydrodynamic stress and competes directly with the nutrient supply. When nutrient supply is strong in the entire domain, QS induction produce more QS up-regulated bacteria to grow robust biofilm colonies upstream. On the other hand, when nutrient supply is weak, QS induction is more prominent downstream. Hydrodynamic stress also alters morphology of the biofilm when the flow is strong in the domain.