Fig 1.

Overview of the general CCM characteristics of α- and β-cyanobacteria, showing the types of Ci transporters typically present in each cyanobacterial type. Typical β-cyanobacteria possess up to two types of CO₂ pumps (green) and up to three types of HCO₃⁻ transporters (orange) and make use of β-carboxysomes (form 1B RubisCO plus ccm gene products), while typical α-cyanobacteria possess only two or three identifiable Ci transporters and make use of α-carboxysomes (form 1A RubisCO plus cso gene products). In the case of Prochlorococcus species (oceanic α-cyanobacteria), the NDH-1-based CO₂ pump genes are entirely missing, and the only candidates for HCO₃⁻ transport are unproven (blue; BicA2 and SbtA2).