Mathematical Modelling of Wrinkle Formation in Bacterial Biofilms
Biofilms are matrix-producing communities of bacterial cells that adhere to surfaces and adopt a multicellular lifestyle. As the predominant life-form of bacteria (estimates suggest that 99% of all bacteria exist in biofilm communities), biofilms play a crucial role in the Earth’s ecosystems, where their existence is known to contribute both beneficial and detrimental effects. One of the defining characteristics of biofilms is heterogeneity in their structure. Indeed, it is commonly observed that biofilms of certain species of bacteria grown under certain conditions can display an unusual wrinkled structure, the pattern of which can vary at different locations throughout the biofilm. It is known that the type of wrinkle morphology displayed can be partially attributed to the expression of particular genes, which also have an effect on the mechanical properties observed in biofilms. Although the functions of wrinkles in biofilms, and the mechanisms controlling their formation, are not fully understood, it is believed that the presence of wrinkles enhances antimicrobial resistance (a property often associated with biofilms). In this thesis we investigate cellular processes and mechanical mechanisms that may contribute to biofilm wrinkle formation. Some emphasis is directed towards the development of wrinkling patterns in biofilms of the Bacillus subtilis bacterium. Particular focus on the role of cell death in initiating pattern formation is explored through the analysis and numerical simulations of mathematical models. In addition we investigate whether classical mathematical tools and techniques that were originally designed to be applied to non-biological structures, and which take into account the mechanical properties of materials, can be implemented and used to explain biofilm wrinkling patterns. Using a mixture of mathematical modelling, analysis and numerical simulations, we conclude that a model description that incorporates the interplay between both biological and mechanical effects may be a useful tool for gaining a better understanding of the biofilm wrinkling process, and thus in the future, may enhance our knowledge of how these complex communities function.
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