The role of the biofilm matrix in structural development.

Although the initiation, development and control of biofilms has been an area of experimental investigation for more than three decades, the role of extra-cellular polymeric substance (EPS) has not been well studied. We present a mathematical description of the EPS matrix to study the development of heterogeneous biofilm morphology. In developing the model, we assume that the biofilm is a biological gel composed of EPS and water. The bacteria are enmeshed in the network and are the producers of the polymer. In response to external conditions, gels absorb or expel solvent causing swelling or contraction due to osmotic pressure gradients. The physical morphology of the biofilm depends on the temperature, solvent composition, pH and ionic concentrations through osmotic pressure. This gives a physically based mechanism for the redistribution of biomass within the biofilm. Analysis of a reduced model indicates that biomass redistribution, through the mechanism of swelling, may induce the formation of isolated towers or mushroom clusters by spatial variation in EPS production which leads to gradients in osmotic pressure.