At the same time, production of diffusible compounds spreading through the substrate by bacterial bodies is both well documented in the literature (see Discussion) and convincingly demonstrated in at least some of our experiments (note gradients of red pigment around R colonies in Figure 2a and 2b, as well as the development of X colonies). We thus proposed the following model, which includes both volatile (airborne) and diffusible (agar-borne) signals. It has been successfully implemented
in a computer program simulating the temporal development of the F colony cross-section profile (Figure 6; Additional file 1; see also Methods). Figure 6 The model. a. Possible states and state transitions of bacterial cells,. All transitions allowed by the formal model are shown, regardless whether they take place during normal colony development; open arrows indicate production of quorum (downwards; arrow size is proportional to the intensity learn more of production) and odor (upwards) signals. Each transition is labeled by the triggering factor (N – colony thickness, Hydroxychloroquine nmr A – time spent in early stationary phase, Qlim – limiting quorum concentration, Olim1 and Olim2 – limiting odor level). b, c. Development of simulated rimmed and rimless colonies. Temporal development of colony size and odor level (b), and colony sections and quorum concentration profiles at selected points during colony
development (c). All values are in relative/arbitrary units. Quorum and sensitivity parameters (quorum limit for inhibition Qlim, limiting odor concentration
for growth reactivation Olim1 and limiting odor concentration Histamine H2 receptor for growth inhibition Olim2) for the simulations are shown in the figure. Other simulation parameters were: maximum colony thickness N = 140; quorum production factor P = 1; odor production factor O = 0.01; stationary to exponential quorum production ratio S = 10; quorum production window A = 5; normalized diffusion factor D = 0.495; diffusion approximated by G = 5 iterations. In the course of the F colony development, a bacterial cell enters a succession of distinct states as follows (Figure 6a). In State 1, corresponding to freshly inoculated or “”young”" growing cells, the bacteria divide exponentially, resulting in a juvenile colony increasing in both its height and diameter. Cells in state 1 produce moderate amounts of a diffusible factor (further referred to as the “”quorum”") that spreads slowly through the substrate and inhibits their own growth if above a threshold concentration (Qlim in the model). When reaching Qlim, or as a result of nutrient limitation (approximated by a maximum colony thickness N in the model), cells stop dividing and enter State 2, corresponding to the early stationary phase and characterized by increased production of the quorum signal. At this stage, the developing colony consists of a core of non-growing cells in state 2, with a margin containing still-growing state 1 bacteria.