Biomineralization-based conversion of carbon dioxide to calcium carbonate using recombinant carbonic anhydrase

Recently, as a mimic of the natural biomineralization process, the use of carbonic anhydrase (CA), which is an enzyme catalyzing fast reversible hydration of carbon dioxide to bicarbonate, has been suggested for biological conversion of CO₂ to valuable chemicals. While purified bovine CA (BCA) has been used in previous studies, its practical utilization in CO₂ conversion has been limited due to the expense of BCA preparation. In the present work, we investigated conversion of CO₂ into calcium carbonate as a target carbonate mineral by using a more economical, recombinant CA. To our knowledge, this is the first report of the usage of recombinant CA for biological CO₂ conversion. Recombinant α-type CA originating in Neisseria gonorrhoeae (NCA) was highly expressed as a soluble form in Escherichia coli. We found that purified recombinant NCA which showed comparable CO₂ hydration activity to commercial BCA significantly promoted formation of solid CaCO₃ through the acceleration of CO₂ hydration rate, which is naturally slow. In addition, the rate of calcite crystal formation was also accelerated using recombinant NCA. Moreover, non-purified crude recombinant NCA also showed relatively significant ability. Therefore, recombinant CA could be an effective, economical biocatalyst in practical CO₂ conversion system.