Induction of calcite precipitation through heightened production of extracellular carbonic anhydrase by CO₂ sequestering bacteria.

The thermo-alkalotolerant bacterium exhibiting heightened extracellular carbonic anhydrase (CA) activity, survived at 100 mM sodium bicarbonateand 5% gaseous CO2 was identified as Bacillus sp. by 16S rRNA sequencing. Extracellular carbonic anhydrase was purified by ammonium sulfate precipitation, gel filtration chromatography and affinity chromatography with a yield of 46.61% and specific activity of 481.66 U/mg. The size of purified carbonic anhydrase was approximately 28 kDa in SDS-PAGE gel filtration and further their role in calcium carbonate production was correlated. The purified enzyme was stable with half-life of 25.36 min at 90 °C and pH 8. KM and Vmax values of the enzyme were 1.77 mg/mL and 385.69 U/mg respectively. The production of calcite was confirmed by Scanning Electron Microscopy (SEM) analysis, FTIR, and Energy-Dispersive X-ray (EDX) analysis. Carbonic anhydrase and calcite deposition coupled with CO2 fixingbacteria is a significant approach for CO2 sequestration.