FIG. 3.

Qualitative steady-state behaviors of (a) design architecture a, constitutive expression of both luxR and luxI; (b) architecture b, constitutive expression of luxR and p(luxI)-mediated expression of luxI; and (c) architecture c, p(luxI)-mediated expression of both luxI and luxR (the dashed line denotes the unstable loci of steady states). Plot d presents a phase plot for a simplified model of the system illustrating the dependence of the steady state on the initial condition (both cell density and 3OC6HSL concentration) for a steady-state cell density of 10⁹ CFU/ml. Solid lines denote the null clines (where the derivative of either the cell density or the 3OC6HSL concentration is zero). Dashed lines denote representative phase traces for this system that were obtained by solving for time courses of the dynamic model with various initial conditions and projecting the solutions onto the cell density-3OC6HSL axes. Arrows denote the directionality of these traces, filled points denote stable attractors, and the unfilled point denotes the unstable attractor. Fluor., fluorescence; A.U., arbitrary units.