Bacterial%20Biofilms:

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Bacterial Biofilms Building Slimy Cities
Gillian Ryan St. Francis Xavier University
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Outline

• ? Background
• ? The Model
• ? Preliminary Results
• ? Future plans

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Biofilm
? Community of microorganisms, including
bacteria, fungi, and protozoa, found in aqueous
environments
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Biofilm
Grown in our lab at StFX
? Picture of a cross sectional slice of a
biofilm, taken with a laser scanning confocal
microscope.
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The Model
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Base Forces
i

• Preserve Linear Momentum
• If rij ? Ro

j
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Quorum Sensing
? On/off switch ? Controls EPS production ?
Dynamically evaluated
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EPS

• 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

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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
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Division Inhibitors
? Spring Force holds dividing bacteria components
together ? Inhibitory emissions dependent on
bacterial neighbors ? Probability of division
depends on inhibitor concentration
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• The Simulation Method
• Molecular Dynamics, specifically Dissipative
  Particle Dynamics (DPD)

GOOD FOR WATER FLOW !
? Velocity-Verlet Algorithm
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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
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Results
Healthy Planktonic Bacteria Healthy Biofilm
Bacteria Inhibited Bacteria Water
1000 water 28 bacteria
Y
Z
Z
X
X
Y
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Results
Healthy Planktonic Bacteria Healthy Biofilm
Bacteria Inhibited Bacteria Water
1000 water 99 bacteria
Y
Z
Z
X
X
Y
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COMING SOON
SURFACES!
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Acknowledgements ? David Pink ? Bonnie Quinn ?
Laura Filion ? Ryan MacDougall ? NSERC