| Summary: | Biofilms are multi-cellular communities of microorganisms attached to surfaces. It has been estimated that about 99% of all bacteria exist in biofilm. Thus to understand the critical role bacteria play in natural and man-made ecosystems, requires a better knowledge of these multi-cellular communities. Biofilms are complex structures comprising cells embedded in a sticky material composed of extracellular polymeric substances (EPS) produced by the cells themselves. The physical structure of the biofilm has been shown to be important to its evolutionary success. EPS is involved in maintaining structural integrity of the biofilm and protects the embedded bacterial cells from adverse elements in the environment. It is known that the morphology and growth rate of biofilms are controlled by a number of factors including environmental conditions and the expression of particular genes. The aim of this thesis was to better understand the links between physical and genetic mechanisms that underpin the function of the EPS matrix. In this thesis, we investigate role of EPS in the structure and development of the biofilm. We do this by adopting an interdisciplinary approach that combines mathematical modelling and analysis, numerical simulation and laboratory experiments. First, we investigate cross-diffusion processes between the cells and the EPS matrix to establish whether structure is mediated in this manner. Then, we study the hypothesis that the cells dominate the growth dynamics in the biofilm, i.e. expansion and structure is determined by cell growth and division. Next, we investigate the hypothesis that the matrix dominates and biofilm expansion is determined by water uptake. Finally, we compare these results to our experimental observations.
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