Identification of a new thermostable and alkali-tolerant α-carbonic anhydrase from Lactobacillus delbrueckii as a biocatalyst for CO2 biomineralization

Abstract

Carbonic anhydrase (CA, EC 4.2.1.1), an ancient enzyme and the fastest among many enzymes, is a useful biocatalyst for carbon capture use and storage (CCUS). The use of alkaline buffers and high temperatures are favorable for biomineralization. Hence, the stability of CA under such harsh conditions is extremely important for its practical application. Herein, we report a new thermostable and alkaline-tolerant α-CA (designated as LdCA), with only 26 % identity to bovine CA (BCA), which was identified by genome mining from Lactobacillus delbrueckii CGMCC 8137. It was overexpressed in Escherichia coli in a soluble form and purified to electrophoretic homogeneity by His-Trap affinity chromatography. The dimer protein had a subunit molecular weight of 23.8 kDa and showed extremely high stability at pH 6.0–11.0 and 30–60 °C. Its activity was maintained even after incubation at 90 °C for 15 min. The half-lives of the enzyme measured at 30, 40, and 50 °C were 630, 370, and 177 h, respectively. At pH 9.0, 10.0, and 11.0, its half-lives were 105, 65, and 41 min, respectively. LdCA was applied at 50 °C to accelerate the formation of calcium carbonate in a vaterite phase. In summary, a new CA with high thermal and alkaline stability was identified from a general bacterium, demonstrating an effective strategy for discovering new and useful biocatalysts.