Fig. 7: An effective PCCM is composed of three essential modules.

a, Schematics of the three essential modules with designated functions (same style as in Fig. 1a). In Chlamydomonas, LCIB can be used for passive uptake of CO₂, which is then trapped in the stroma as HCO₃⁻ (module i); BST allows stromal HCO₃⁻ to diffuse into the thylakoid lumen where CAH3 converts HCO₃⁻ into CO₂ (module ii); and a starch sheath and thylakoid stacks could act as diffusion barriers to slow CO₂ escape out of the pyrenoid matrix (module iii). b, Histograms of normalized CO₂ fixation flux for CCM configurations without (left, grey) or with (right, coloured) the respective module. We tested 216 CCM configurations by varying the presence and/or localization of enzymes, HCO₃⁻ channels and diffusion barriers in the model (see Supplementary Fig. 26).