Extended Data Fig. 6: Setup of the reaction-diffusion simulation of CtrA activation pathway.

a. A simplified schematic of the reaction and diffusion events used in our CtrA activation model. Dotted red arrows indicate CckA, ChpT, and CckA binding to either the new pole (NP) or the old pole (OP) species. The width of the arrow represents the strength of binding, with thicker arrows for tighter binding. The colored edges out of CckA (blue), ChpT (orange), and CtrA (green) boxes indicate diffusion inside the pole and in the body of the cell. The length of the arrow represents the rate of diffusion, with shorter arrows representing slower diffusion. Phosphotransfer reactions are shown in black. Each arrow is labeled with a reaction number from 1 to 39. Information on each reaction is found in Supplementary Table 7. b. A complete schematic of the phosphotransfer reactions including binding and transfer events. Reaction numbers match the simplified schematic in (a). c. Concentrations of each molecular species in the system were modeled as a function of position along the long axis of the cell and time. The governing partial differential equation (PDE) for each species was approximated as a set of ordinary differential equations (ODEs). The spatial dimension of a 4 μm cell was discretized into n = 80 bins, each representing a 0.05 μm Δx section of the cell. Each species is broken into n sub-species, one per bin. The simulation advances in 0.1 second steps. We use the second-order center difference formula to approximate the Laplacian operator and convert each PDE into a set of ODEs (Supplementary Note 2.2, equation S7). d. Simulation results with wildtype parameters (Fig. 3a) showing steady-state protein concentrations for CckA (blue), ChpT (orange), and CtrA (green) as a function of distance from the new pole in the predivisional cell.