Fig 7. Steady-state CoSMO growth rate can be predicted from parameters measured in chemostats.

(A) Steady-state CoSMO growth rate on agarose pad. Preconditioned L⁻A⁺ and A⁻L⁺ were mixed at approximately 1:1 ratio, and 15 μL of 4 × 10⁴ total cells was spotted on the center of agarose pads (inset), forming an inoculum spot of radius 4 mm (S24A Fig; Methods, “Quantifying spatial CoSMO growth dynamics”). Periodically, cells from pads were washed off into water and subjected to flow cytometry. (B) A comparison of model predictions and experiments. Steady-state growth rate of well-mixed CoSMO was calculated from Eq 5 or Eq 17 (with nearly identical results) when we borrowed release rates from a different strain background in starved batch culture (gray; Model i in Fig 1B), when all parameters were measured from the correct strain background in batch cultures (blue; Model ii in Fig 1B), and when all parameters were measured from the correct strain background in chemostats (green; Model iii). A partial differential equation model (i.e., the spatial version of Model iii) was simulated for spatial CoSMO under various experimental configurations, yielding similar predictions on spatial CoSMO growth rate (S23 Fig; S6 Code; S7 Code). The average value was plotted here (brown). In simulations, CoSMO grew at a similar rate in a spatially structured environment as in a well-mixed environment. This is because in spatial CoSMO, concentrations of metabolites eventually became uniform in the agarose and in the community (S25 Fig) and because the two strains formed small (tens of micrometers) patches that were intermixed [32]. The green error bar (95% confidence interval) was calculated from uncertainties in parameter estimations (i.e., 2 SEMs in Table 1) via the method of error propagation (Methods, “Calculating steady-state community growth rate”). Under various experimental configurations (Methods, “Quantifying spatial CoSMO growth dynamics”), steady-state CoSMO growth rates were similar, and the average value and 2 standard deviations from 11 independent experiments were plotted (purple; S4 Table). All data can be found in S7 Data. CoSMO, Cooperation that is Synthetic and Mutually Obligatory; SEM, standard error of the mean; sim., simulation.