CO2 mineralization by the recombinant strains expressing thermostable carbonic anhydrases

Abstract

Carbonic anhydrase (CA), one of the fastest enzymes, is involved in the reversible hydration of CO2 to bicarbonate ions and protons (CO2+H2O &#8646 HCO3- + H+). CO2 mineralization involves the precipitation of CO2 to calcium carbonate (CaCO3) with the aid of carbonic anhydrase (CA). In this study, we selected thermostable CAs from thermophilic microbes such as Sulfolobus solfataricus (optimal growth temperature: 85℃) and Metallosphera sedula (73℃), and a mesophilic CA from Acetobacterium woodii (37℃) to test CA-mediated CO2 to calcium carbonate (CaCO3) with the aid of carbonic anhydrase (CA). genes were introduced into T. onnurineus NA1 by double-crossover homologous recombination and the genes were overexpressed under the control of a strong promoter. CA activity of recombinant strains was determined by measuring the change in pH and S. solfataricus CA and M. sedula β-CA showed higher activity than others at 70℃ and 80℃. CO2 mineralization activity of cell lysate of recombinant strains was investigated using bioreactors at 50℃ by adding 20mM CaCl2 and CAs tested showed 10 - 15% increase of CO2 capture efficiency. For cost-effective CO2 mineralization, seawater was substituted for 1M Tris-HCl buffer and pH was controlled by 2N NaOH and 6 - 7% increases were obtained in CO2 capture efficiency for recombinant CAs. For a further study, these results are to be applied to the actual process, where H2 and CO2 areCO3) with the aid of carbonic anhydrase (CA). In this study, we selected thermostable CAs from thermophilic microbes such as Sulfolobus solfataricus (optimal growth temperature: 85℃) and Metallosphera sedula (73℃), and a mesophilic CA from Acetobacterium woodii (37℃) to test CA-mediated CO2 to calcium carbonate (CaCO3) with the aid of carbonic anhydrase (CA). genes were introduced into T. onnurineus NA1 by double-crossover homologous recombination and the genes were overexpressed under the control of a strong promoter. CA activity of recombinant strains was determined by measuring the change in pH and S. solfataricus CA and M. sedula β-CA showed higher activity than others at 70℃ and 80℃. CO2 mineralization activity of cell lysate of recombinant strains was investigated using bioreactors at 50℃ by adding 20mM CaCl2 and CAs tested showed 10 - 15% increase of CO2 capture efficiency. For cost-effective CO2 mineralization, seawater was substituted for 1M Tris-HCl buffer and pH was controlled by 2N NaOH and 6 - 7% increases were obtained in CO2 capture efficiency for recombinant CAs. For a further study, these results are to be applied to the actual process, where H2 and CO2 are produced by Thermococcus onnurineus NA1, to capture CO2 emitted.