The fluid dynamics of nascent biofilms

Bacteria are often found in surface associated structures called biofilms, composed of individual bacterial cells along with various extra-cellular components. They are a leading cause of antibiotic resistant infections and are a global issue. In this thesis, the focus is on the very early stages of biofilm formation and, in particular, the effect of bacterial motility on biofilm formation is investigated. Various microscopy techniques are used to determine that surface attached bacteria maintain moving flagella, which induce a flow around the bacteria. The flow due to such surface-attached bacteria has not previously been reported. In this thesis, holographic microscopy is used to determine the shape of the flow. The flow is found to be different when cells are exposed to a lactam analogue (which is thought to disrupt biofilm formation by interfering with cell-cell communication). In this thesis, a suggested explanation for this change in flow is an increase in flagellar reversal rate when the cells are exposed to the lactam analogue compared to a control set is presented. A simple model of the surface-attached cell with a motile flagellum is developed to capture the key elements of the flow. This simple model relies on singularity solutions to the Stokes equations and has low computational expenditure. This ease of computation allows the simulation of multiple cells so that the effect of the cells' induced flow on cell-cell communication can be investigated. Particle dispersion is found to be enhanced in the presence of simulated cells with the control reversal rate in comparison to those with the lactam reversal rate. This suggests that one effect of the lactam analogue is to lessen the transport of cell-cell communication molecules.