Abstract
Bio-calcification, known as microbiologically induced calcium precipitation, is an important process of the global carbon cycle. A large number of microorganisms exhibit this ability, including cyanobacteria. Even though the process was realized a long time ago, the detailed mechanism is still unclear. In this paper, we investigate the key role of extracellular carbonic anhydrase during bio-calcification of Synechocystis sp. FACHB 898. Detailed studies revealed that the precipitation of CaCO3 was significantly hindered when the function of extracellular carbonic anhydrase in Synechocystis sp. was inhibited. Furthermore, the reduction of calcium concentration in solution was significantly correlated with the reduction of bicarbonate concentration as 1 : 2. The results suggested that extracellular carbonic anhydrase of cyanobacteria enhanced CaCO3 precipitation from calcium and bicarbonate through facilitating the proton consumption during transformation of bicarbonate to carbon dioxide.