Catalyzes the reversible hydration of CO(2) to H(2)CO(3). The main role may be to provide inorganic carbon for the bicarbonate-dependent carboxylation reactions catalyzed by pyruvate carboxylase, acetyl-CoA carboxylase and carbamoyl-phosphate synthetase (By similarity). Involved in osmoadaptation. H(+) + hydrogencarbonate = CO2 + H2O Binds 1 zinc ion per subunit. Down-regulated when grown with elevated levels of potassium chloride. Belongs to the beta-class carbonic anhydrase family. Extended N-terminus.