Two-Dimensionality of Yeast Colony Expansion Accompanied by Pattern Formation
Figure 2
Mathematical model of colony expansion.
(A–C) A snapshot of the colonies at the end of simulation. Although these simulations are started with circular colonies, over time petals appear. The color scale represents cell density (arbitrary units). (D–F) The maximum colony area is higher upon higher initial glucose concentration, in agreement with the experimental results in Fig. 1. The dimensionless “colony area ratio” was the ratio of colony area to the area of simulation box, and glucose concentration corresponded to the initial value of glucose in the simulation, and was chosen as a constant over space. Time is a rescaled variable measured in arbitrary units. (G–I) Simulated colony irregularity (P2A) plotted as a function of time. Similar to experiments (Fig. 1), in our model P2A is initially at a basal level and then increases abruptly to a large value. This increase in P2A corresponds to petal formation and occurs as a result of competition over glucose among cells that make up the colony rim. Interestingly, the maximum value of P2A decreases with increasing glucose levels. This result is likely due to decreased intercellular competition over nutrients in the early stages of expansion and is compatible with experiments in Fig. 1, where colonies exhibit less structure as glucose levels increase.