Characterization of novel carbonic anhydrase from halophilic bacterial isolates and it’s role in microbially induced calcium carbonate precipitation

Abstract

Microbially Induced Calcium Carbonate Precipitation (MICCP) has been widely used technology now a day for remediation of building structures. It has been found that along with Urease, Carbonic anhydrase (CA) is also involved in the carbonate precipitation process. In the present study, CA was isolated and characterised from halophilic bacteria (A3-5 and A1-4) and its role in microbially induced calcium carbonate precipitation was studied. The catalytic activities for the crude and lyophilised CA were estimated by using p-Nitrophenyl Acetate (p-NPA) as the substrate. KM and Vmax values for crude enzyme were found to be 0.31 mM and 1.88 µmoles/min and 0.67 mM and 1.49 µmoles/min, respectively for A3-5 and A1-4. The lyophilized enzyme showed an increased KM value of 0.20 mM and 0.37 mM for A3-5 and A1-4, respectively whereas Vmax value was found to be slightly lower for A3-5 (1.14 µmoles/min) but increased in case of A1-4 (1.69 µmoles/min) at 25◦C. The optimum range of pH temperature for the crude CA was found to be between 7 - 9 and 50°C - 60°C respectively. The crude CA was investigated to enhance CaCO3 precipitation. MICCP was also studied at varying pH and morphologies of the different carbonate polymorphs formed were studied. Best MICCP activity by CA influenced precipitation was obtained at 100 mM CaCl2 + 75mM NaHCO3 + 100 µM ZnSO4 at pH 9. It was concluded that the extracellular CA from halophilic bacteria has the potential for efficient calcium carbonate precipitation and hence can be looked as a new tool in MICCP.