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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 Division Quorum Sensing Exopolysaccharides Chemotaxis 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 r-ij i Preserve Linear Momentum Ro Ri R j j If rij Ro : Ro r Fi C ( Ro rij )rˆij 1 2 Fi ( Ro rij ) ij t rˆij D 2 Fi ( Ro rij ) (rˆij v~ij )rˆij R 2kbT 2 v~ij v~i v~j ij ji Quorum Sensing: On/off switch Controls EPS production Dynamically evaluated EPS: Only produced by biofilm bacteria Amount of EPS emitted is a constant EPS spring force binds bacteria to EPS carrying water and EPScarrying water to EPS-carrying water 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 FA1 FA2 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 GOOD Dynamics (DPD) FOR WATER FLOW ! Velocity-Verlet Algorithm 1 2 ri (t t ) ri (t ) tvi (t ) (t ) ai (t ) 2 v~i (t t ) vi (t ) tai (t ) Fi ai (t t ) massi 1 vi (t t ) vi (t ) (t )( ai (t ) ai (t t )) 2 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 Healthy Planktonic Bacteria Results: Healthy Biofilm Bacteria 1000 water Inhibited Bacteria 28 bacteria Y Water Z X Z X Y Healthy Planktonic Bacteria Results: Healthy Biofilm Bacteria 1000 water Inhibited Bacteria 99 bacteria Y Water Z X Z X Y COMING SOON: SURFACES! Acknowledgements: David Pink Bonnie Quinn Laura Filion Ryan MacDougall NSERC