Reversible hydration of carbon dioxide. Important for growth on acetate (PubMed:8041719). As a probably extracellular enzyme, it may support a H(+)/CH(3)COO(-) symport mechanism and/or conversion of CO(2) to HCO(3)(-), removing excess CO(2) produced by growth on acetate (Probable). H(+) + hydrogencarbonate = CO2 + H2O Binds 1 Zn(2+) per subunit, at the subunit interface. Homotrimer. When isolated from M.thermophila. Belongs to the gamma-class carbonic anhydrase family. Extended N-terminus.