Reversible hydration of carbon dioxide (PubMed:14729686). Essential for photosynthetic carbon dioxide fixation, supplies CO(2) to RuBisCO (ribulose bisphosphate carboxylase, cbbL-cbbS) in the carboxysome (Probable). H(+) + hydrogencarbonate = CO2 + H2O Binds 1 Zn(2+) per monomer. Homodimer. This cyanobacterium makes alpha-type carboxysomes. Belongs to the beta-class carbonic anhydrase family. CsoSCA subfamily.