(A) Experimental data, adapted from (Mashburn-Warren et al., 2010), show that exogenous XIP (in defined medium) stimulates more transformation in the wild-type S. mutans than in a ΔcomS mutant. Studies by Mashburn-Warren et al. were performed in triplicate, leading to uncertainties (standard deviation) similar to the size of the plotting symbols.
(B) Simulation of a hybrid of the two feedback models in FIGURE 2, where extracellular XIP can cross the cell membrane but ComS cannot. Environmental XIP enters the cell and stimulates the intracellular ComS feedback loop, leading to greater activation of comS and comX in the wildtype (blue curve) than in ΔcomS (red curve).
(C) Diagram of hybrid model. Model details and parameters are given in Supplemental information.