Reversible hydration of carbon dioxide. This bacteria encodes at least 3 CA enzymes (PubMed:20400567). Essential for chemolithotrophic 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. Inhibited by ethoxyzolamide and dithiothreitol (in crude extracts upon expression in E.coli). Homodimer. This bacterium makes alpha-type carboxysomes. Induced by growth in low levels of dissolved inorganic carbon (DIC) (at protein level). Cells do not grow in low DIC levels. Cells lose carboxysomes when grown under low DIC conditions. Accumulates intracellular DIC normally, poor CO(2) fixation. Belongs to the beta-class carbonic anhydrase family. CsoSCA subfamily.