Bacterial Biofilms: Building Slimy Cities Gillian Ryan St. Francis Xavier University Outline: Background The Model Preliminary Results Future plans Biofilm: Community of microorganisms, including bacteria, fungi, and protozoa, found in aqueous environments Exopolysaccharides Division Chemotaxis Quorum Sensing Biofilm: Picture of a cross sectional slice of a biofilm, taken with a laser scanning confocal microscope. Grown in our lab at StFX The Model: Base Forces i j r ij - Preserve Linear Momentum If rij Ro : Quorum Sensing: On/off switch Controls EPS production Dynamically evaluated Only produced by biofilm bacteria Amount of EPS emitted is a constant EPS spring force binds bacteria to EPS carrying water and EPS- carrying water to EPS-carrying water EPS: Attractants: Amount of positive chemotactic signals emitted inversely related on number of bacterial neighbors Carried by water, which attracts bacteria Force is proportional to amount of attractant in water F A1 F A2 Division & Inhibitors: Spring Force holds dividing bacteria components together Inhibitory emissions dependent on bacterial neighbors Probability of division depends on inhibitor concentration The Simulation Method: Molecular Dynamics, specifically Dissipative Particle Dynamics (DPD) GOOD FOR WATER FLOW ! Velocity-Verlet Algorithm The Simulation: 1000 water spheres and 1 free bacterium World is initially a 10x10x10 micron box with periodic boundary conditions System is initialized with zero linear momentum X X Y YZ Z Results: 1000 water 28 bacteria Healthy Planktonic Bacteria Healthy Biofilm Bacteria Inhibited Bacteria Water X X Y YZ Z Results: 1000 water 99 bacteria Healthy Planktonic Bacteria Healthy Biofilm Bacteria Inhibited Bacteria Water COMING SOON: SURFACES! Acknowledgements: David Pink Bonnie Quinn Laura Filion Ryan MacDougall NSERC