ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

g [-]
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FLOplus vs. FLOplus
FLOplus vs. FLOminus
FLOminus vs. FLOplus
FLOminus vs. FLOminus
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0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
d [mean cell diameter]
Figure 2: Radial distribution function for t = 18 : 03h for a simulation with Young’s modulus E = 6.4kPa.
4 RESULTS AND DISCUSSION
4.1 Natural Young’s Modulus of yeast
Since it is not currently feasible to simulate how yeast grows and sorts with the natural Young’s
modulus of the cells because the time-step would have to be prohibitively low 1 , we analyzed the
influence of stiffness on sorting behavior. The results (see figure 3 (a) - (e)) show that increased
stiffness leads to better sorting, but that the differences become negligible in the kPa range. The
differences between 1.6 kPa to 6.4 kPa Young’s modulus are comparable to the differences of two
simulations with the same Young’s modulus and a different random seed. The figures shown
average over six different realizations of the simulation.
4.2 Sorting by adhesion strength
In absence of reliable measurements of adhesion strength incurred by the expression or nonexpression
of the FLO1 protein, we simulated several absolute and relative adhesion strengths
for both types. Strongest sorting as well as most dissociated f lo− cells were found, if the f lo− strain had an adhesion energy σ−− = 0J/m2 (figure 4). We set the adhesion energy between the
two different types σ+− = σ+++σ−− , since the FLO1 proteins not only adhere to each other, but
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also to other cell wall proteins. Our results indicate, that sorting still occurs for differences in
adhesion strength σ++ vs. σ−− as small as two-fold or even smaller depending on the definition
of “sorted”. As described above, the model only takes Brownian motion and movement due to
budding into account (the latter of which contributes significantly to the sorting, data not shown).
1 estimated time for one simulation to complete: 190 days