The biomimetic approach represents an interesting strategy for carbon dioxide (CO₂) capture, offering advantages over other methods, due to its specificity for CO₂ and its eco-compatibility, as it allows concentration of CO₂ from other gases, and its conversion to water soluble ions. This approach uses microorganisms capable of fixing CO₂ through metabolic pathways or via the use of an enzyme, such as carbonic anhydrase (CA, EC 4.2.1.1). Recently, our group cloned and purified a novel bacterial α-CA, named SspCA, from the thermophilic bacteria, Sulfurihydrogenibium yellowstonense YO3AOP1 living in hot springs at temperatures of up to 110 °C. This enzyme showed an exceptional thermal stability, retaining its high catalytic activity for the CO₂ hydration reaction even after being heated at 70 °C for several hours. In the present paper, the SspCA was immobilized within a polyurethane (PU) foam. The immobilized enzyme was found to be catalytically active and showed a long-term stability. A bioreactor containing the “PU-immobilized enzyme” (PU-SspCA) as shredded foam was used for experimental tests aimed to verify the CO₂ capture capability in conditions close to those of a power plant application. In this bioreactor, a gas phase, containing CO₂, was put into contact with a liquid phase under conditions, where CO₂ contained in the gas phase was absorbed and efficiently converted into bicarbonate by the extremo-α-CA.

A new carbonic anhydrase (CA, EC 4.2.1.1) from the thermophilic bacterium Sulfurihydrogenibium yellowstonense YO3AOP1 was identified and characterized. The bacterial carbonic anhydrase gene was expressed in Escherichia coli yielding an active enzyme, which was purified in large amounts. The recombinant protein (SspCA) was found to belong to the α-CA class and displays esterase activity. The kinetic parameters were determined by using CO₂ and p-nitrophenylacetate (p-NpA) as substrates. The bacterial enzyme presented specific activity comparable to that of bovine carbonic anhydrase (bCA II) but it showed biochemical properties never observed for the mammalian enzyme. The thermophilic enzyme, in fact, was endowed with high thermostability and with unaltered residual activity after prolonged exposure to heat up to 100°C. SspCA and the bovine carbonic anhydrase (bCA II) were immobilized within a polyurethane (PU) foam. The immobilized bacterial enzyme was found to be active and stable at 100°C up to 50 h.

Vibrio cholerae, a Gram-negative bacterium, is the causative agent of cholera and colonizes the upper small intestine where sodium bicarbonate is present at a high concentration. Sodium bicarbonate is a potential inducer of virulence gene expression. Bacteria can increase cytosolic bicarbonate levels through the existence of transporter family proteins or through the action of metalloenzymes, called carbonic anhydrases (CAs, EC 4.2.1.1). Vibrio cholerae, lacking of transporter proteins in its genome, utilizes the CA system to accumulate bicarbonate into the cell suggesting a pivotal role of this metalloenzymes in the microbial virulence. Here, we report for the first time the characterization of the α-CA of V. cholerae (VchCA), which has been identified by translated genome inspection. The α-CA encoding gene was cloned and expressed in Escherichia coli and the recombinant protein purified to homogeneity. This investigation aimed to study the biochemical properties of VchCA and to provide preliminary insights in the field of this pathogen virulence. VchCA has a low esterase activity with 4-nitrophenyl acetate as substrate, and a high activity for the hydration of CO₂ to bicarbonate.