Fig. 2.

Simulated biofilm competitions between QS and non-QS cells. (A) QS cells shown in green produce AI at a constant rate; arrows indicate AI diffusion. QS cells adjust their matrix bias based on local AI concentration. (B) Snapshot of a pairwise competition after 1,000 simulation timesteps. Green QS cells produce and detect AI and adjust their matrix bias from $b_{\text{max}}=0.9$ at zero AI down to $b_{\text{min}}=0.1$ at high AI (see Eq. 1). Non-QS cells (red) do not produce AI and have a fixed matrix bias of 0.4. ${\text{O}}_2$ diffuses from above as in Fig. 1, but the color shade now indicates local AI concentration (in arbitrary units as described in SI Appendix). (C) Snapshot of the same competition in B after $\mathrm{3,000}$ timesteps. (D) Mean of the natural logarithm of the final ratio of number of QS cells to number of fixed-matrix-bias cells (green curve). For comparison, the results of the pairwise competitions for the optimal fixed-strategy matrix bias of 0.7 are also shown. The error bars indicate standard deviations of log ratios; 42–65 simulations were performed for each competition.