Fig. 2. Organic chemical production by synthetic phototrophic communities.

a Production capabilities were evaluated for all SPCs by iteratively simulating the synthesis of metabolites while maximizing for growth. Metabolite production rates were sorted and plotted for each synthetic phototrophic community (SPC). Metabolites feasible to produce were identified by having production rates over 1 × 10⁻² mmol gDW⁻¹ h⁻¹. b Overall production capabilities for butanal, ethanol, formaldehyde, methanol, and succinate. The bar plot shows the predicted maximum production rate achieved by each SPC. The predicted abundance (growth rate) of community members is shown for S. elongatus cscB⁺(green) and for heterotrophs (blue B. subtilis, yellow E. coli K-12, purple E. coli W, or pink Y. lipolytica). Microbial communities containing E. coli strains showed high formaldehyde production potential. c, d Predicted growth rates and associated metabolic exchanges for the SPC composed of S. elongatus cscB⁺ and either E. coli K-12 (c) or E. coli W (d) while producing butanal. CM-models enable prediction of substrate resource allocation into growth or into target metabolites. Production of metabolites reduces the growth of community members as observed in the growth rate plots. Here, the overall growth rate of the community (black line) and each member (green S. elongatus cscB⁺ paired with yellow or purple for E. coli K-12 or E. coli W, respectively) were simulated. Simulations show that at higher butanal production rates the heterotroph will be outcompeted by the phototroph before the SPC crashes. The complete-linkage clustering based on the metabolic exchange predictions shows associations among metabolites listed on the y-axis and butanal production rates from left to right. Growth rate predictions were remarkably associated with a specific metabolic exchange. For example, the synthesis of butanal by the E. coli K-12 SPC was possible by increasing the flux exchange of metabolites such as isoleucine (ILEL), phenylalanine (PHEL), serine (SERL), and threonine (THRL), while for the E. coli W SPC butanal production relied heavily on L-glutamine exchange (GLUL). Metabolic exchanges of all SPCs are given in Supplementary Fig. 3.