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