Bacterial extremo-α-carbonic anhydrases from deep-sea hydrothermal vents as potential biocatalysts for CO2 sequestration.

Carbonic anhydrase (CA) is an enzyme that rapidly catalyzes the reversible hydration of carbon dioxide (CO2) in aqueous solutions. Recent progresses in CA research suggest that this biocatalyst can be used as an alternative or an additive for chemical CO2 capture, which is considered an essential green route for the reduction of anthropogenic CO2 emissions. However, the facilities in which CA will most likely be used usually operate under high temperature conditions, requiring a highly thermostable CA. Here, we attempted to find and characterize α-CAs originated from Persephonella marina and Thermovibrio ammonificans, thermophilic Gram-negative bacteria in deep-sea hydrothermal vents. The recombinant α-CAs expressed in Escherichia coli showed catalytic efficiencies better than the previously characterized thermophilic β- and γ-CAs from archaea, and their activities were significantly increased at higher temperatures. Remarkably, these enzymes exhibited outstanding thermostability (stable up to at least 80 °C). Through long-term stability tests at 40 °C and 60 °C, we discovered that the novel α-CA of T. ammonificans might be the most thermostable CA ever characterized. Also, the recombinant CAs successfully accelerated CO2 sequestration in CaCO3, more efficiently than mesophilic bovine CA under high temperature condition. Collectively, these results demonstrate that the α-CAs of thermophilic bacteria from deep-sea hydrothermal vents are promising biocatalysts for practical industrial CO2 capture in terms of both activity and stability.