Figure 4
Access to AHL and access to nutrients determines P CRIT during periodic spatial disturbance. (A) P CRIT of engineered bacteria shaken at different frequencies and agar densities. At 1/hr, 9/hr and 12/hr, P CRIT was identical in all agar densities (p ≥ 0.36). At 3/hr and 6/hr, P CRIT decreased with increasing agar density (p ≤ 0.04). Raw data in Supplementary Fig. S1. P CRIT as a function of δ in Supplementary Fig. S2. Two-tailed t-tests for P CRIT in Supplementary Tables S1 and S2. For panels with experimental data, SD from a minimum of three biological replicates. (B) Growth rate of engineered bacteria at different frequencies and agar densities. Bacteria in medium with 0% agar had a higher growth rate than bacteria in 0.2% and 0.4% agar (p ≤ 0.002, two-tailed t-test). p = 0.53 when 0.2% and 0.4% agar are compared to each other. (C) OD600 reached by bacteria after growing for 16 hours in medium obtained from previous cultures with 0% and 0.4% agar. In both cases, the medium was obtained at 0 cm and 0.5 cm from the initial point of inoculation. In 0% agar, OD600 was the same after 16 hours (p = 0.574). In 0.4% agar, OD600 was higher in the sample taken 0.5 cm away from the initial point of inoculation (p = 0.004, Methods and Supplementary Results). (D) Simulation results demonstrating how P CRIT is affected by shaking frequency (Equations (1–3), see Methods). (E) Values of δ from experimental data (left panel) and in our model (right panel, see Methods). For experimental data, p ≤ 0.05 for comparisons within and between different frequencies and agar densities except p = 0.27 when 1/hr and 12/hr are compared in medium with 0.4% agar (two-tailed t-test). (F) Values of α in our model that were qualitatively fit to Fig. 2C (see Supplementary Results). (G) Schematic of mechanism. With low shaking frequency, bacteria are clustered, increasing AHL access but reducing nutrients access through increased competition. With high shaking frequency, AHL access is reduced, but access to nutrient is increased through decreased competition. The non-linearity of these opposing trends cause changes in P CRIT at intermediate shaking frequency.
