Extracellular carbonic anhydrases of the stromatolite-forming cyanobacterium Microcoleus chthonoplastes

Abstract

Active extracellular carbonic anhydrases (CAs) were found in the alkaliphilic stromatolite-forming cyanobacterium Microcoleus chthonoplastes. Enzyme activity was detected in intact cells and in the cell envelope fraction. Western blot analysis of polypeptides from the cell envelope suggested the presence of at least two polypeptides cross-reacting with antibodies against both α and β classes of CA. Immunocytochemical analysis revealed putative α-CA localized in the glycocalyx. This α-CA has a molecular mass of about 34 kDa and a pl of 3.5. External CAs showed two peaks of activity at around pH 10 and 7.5. The possible involvement of extracellular CAs of M. chthonoplastes in photosynthetic assimilation of inorganic carbon and its relationship to CaCO3 deposition during mineralization of cyanobacterial cells are discussed. © 2007 SGM.