A model showing the potential role of Cah6 and other known CAs in the operation of CCM in C. reinhardtii. The font sizes of CO2 and HCO3− indicate the relative concentrations of these Ci species. Cyt CA? represents a putative cytoplasmic carbonic anhydrase. P, Cy, Ch, and Py represent periplasm, cytoplasm, chloroplast, and pyrenoid, respectively. Cah1 and Cah3 represent the periplasmic and thylakoid CAs, respectively. Putative HCO3− transporters are denoted by small black circles.