Novel alkalistable α-carbonic anhydrase from the polyextremophilic bacterium Bacillus halodurans: characteristics and applicability in flue gas CO2 sequestration.

The emissions of CO2 into the atmosphere have been constantly rising due to anthropogenic activities, which have led to global warming and climate change. Among various methods proposed for mitigating CO2 levels in the atmosphere, carbonic anhydrase (CA)-mediated carbon sequestration represents a greener and safer approach to capture and convert it into stable mineral carbonates. Despite the fact that CA is an extremely efficient metalloenzyme that catalyzes the hydration of CO2 (CO2 + H2O ↔ HCO3 (-) + H(+)) with a kcat of ∼10(6) s(-1), a thermostable, and alkalistable CA is desirable for the process to take place efficiently. The purified CA from alkaliphilic, moderately thermophilic, and halotolerant Bacillus halodurans TSLV1 (BhCA) is a homodimeric enzyme with a subunit molecular mass of ~37 kDa with stability in a broad pH range between 6.0 and 11.0. It has a moderate thermostability with a T1/2 of 24.0 ± 1.0 min at 60 °C. Based on the sensitivity of CA to specific inhibitors, BhCA is an α-CA; this has been confirmed by nucleotide/amino acid sequence analysis. This has a unique property of stimulation by SO4 (2-), and it remains unaffected by SO3 (2-), NOx, and most other components present in the flue gas. BhCA is highly efficient in accelerating the mineralization of CO2 as compared to commercial bovine carbonic anhydrase (BCA) and is also efficient in the sequestration of CO2 from the exhaust of petrol driven car, thus, a useful biocatalyst for sequestering CO2 from flue gas.