A model of biofilm growth and structural development

The initiation, development and control of bacterial colonies termed biofilms has been an area of experimental investigation for more than two decades. Experimentalists have concentrated their research on the components of biofilms including bacteria, substrates and effluent products. However, the role of extra-cellular polymeric substance (EPS) has not been well studied.; Experiments have indicated that the physically heterogeneous structure of the biofilm is regulated by both the external bulk flow and internal processes such as growth and quorum sensing. It has been hypothesized that the physical structure of biofilms benefits the bacteria in many ways such as increasing nutrient transport and waste removal. To investigate this hypothesis, biofilm models have been used by investigators to study the dynamic behavior of bacteria, substrate, waste products and biofilm structure. However, these models neglect EPS although up to 90% of biofilm biomass is comprised of EPS.; We present a model of biofilm behavior, preliminary analysis of which, has indicated two mechanisms that may cause biofilm heterogeneity. One mechanism involves differential growth of biofilm. If the interface between the biofilm and the bulk region is irregular, bacteria in the peaks of the interface have more ready access to diffusing substrate than those in the troughs. Therefore, these bacteria reproduce at a faster rate, increasing the local network density. Since the network is chemically active, this increase induces an osmotic pressure causing the network to swell. Swelling moves the biofilm interface, reinforcing the nonuniformity.; The second mechanism is due to the frictional interaction between the biofilm and the bulk flow. As the bulk fluid moves, it drags the polymer network along with it. This network displacement induces stress on the network due to tangling and cross-linking interaction within the network. In this manner, the network distribution is altered increasing the density of the network in some areas while decreasing it in others. The bulk fluid moves through the regions of low volume fraction more easily, thus the fluid flow is larger there. This reinforces the displacement of network creating channels through the biofilm.; We present the mathematical model and preliminary analysis of structural development. The model accounts for the physical and chemical structure of the EPS and the interaction between the bulk flow and the biofilm growth dynamics. We claim that this model reflects the physical structure of the biofilm more realistically than previously developed models and may be useful to investigate the biological and physical mechanisms that induce biofilm heterogeneity.