FIG 2 .

Pattern formation by colony growth model coupled with the positive-feedback motif that shows bistability. The repressor was removed by setting α_R = 0. There are about 80,000 cells in the biggest colonies. The aspect ratio of a cell just after cell division is 2:1, and the diameter of the biggest colony equals about 530 times the length of the shorter axis of the cell. The simulation is started with a cell which does not contain any A protein. (A) Time series of colony and pattern development using parameter values α_A = 240, b_A = 0.03, K_A = 36, and Γ_A = 240, measured in units of time scale (the generation time at maximum growth) and units of concentration (1 molecule per cell volume Ω₀). For the colony snapshots, the brightness is proportional to the density of the A proteins in cells, and the maximum level is tuned so that the cell with the highest concentration in time 20 (${\varphi }_A^{max}\approx 100$) appears as a fully saturated spot. (B) Representative result of simulations performed using a lower production rate of the A protein and more frequent switching between the high and low states (α_A = 60, b_A = 0.03, K_A = 9, and Γ_A = 2). The brightness was normalized by the maximum concentration${\varphi }_A^{max}\approx 35$.