Fig. 5.

Proposed box model based on experimental results. (A) Experimental results (circles and crosses) plotted onto traditional box model outputs (solid and dashed lines) for WT and ANC, respectively, if C_i uptake is all CO₂. See SI Appendix, Table S11 for quantification of uncertainty. Colors indicate growth conditions as in Fig. 2. The red shaded region demarcates the physiologically infeasible region where f > 1. (B) Our proposed box model architecture. Subscripts indicate external (ext), internal (int), carboxysome (carb), and fixed (fixed) carbon pools. Fluxes are denoted by Φ where subscripts indicate fluxes into the cell (in), out of the cell (Loss1, Loss2), into the carboxysome (VCA for Vectoral Carbonic Anhydrase), and into fixed biomass (Rubisco), each with a corresponding isotopic fractionation denoted with ε. Loss fluxes were assumed to have no isotopic fractionation. In this model, f₁ is defined as Φ_Loss1/Φ_in, and f₂ is defined as Φ_Loss2/Φ_VCA. (C) Experimental results plotted onto proposed box model outputs for f₁ = 0.1; colors and symbols are the same as Panel A; see SI Appendix, Table S11 for quantification of uncertainty. ε_p is defined as the difference in δ¹³C between C_ext and C_fixed. Here only results for f₁ = 0.1 are shown; see SI Appendix, Supplementary Text for full description of model assumptions and results.