Transcript biopres
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