Characteristics of recombinant α-carbonic anhydrase of polyextremophilic bacterium Bacillus halodurans TSLV1

Carbonic anhydrase (CA) is a biocatalyst that catalyzes the hydration of CO2 to bicarbonate and protons, thus useful in mitigating green house effect by sequestering CO2 from various point sources. An alkalistable and moderately thermostable α- carbonic anhydrase encoding gene (BhCA) from Bacillus halodurans TSLV1 has been cloned and expressed in Escherichia coli. A 31.4-fold enhancement in CA production was achieved due to cloning and expression in E. coli. About 50% of the CA produced was secreted when recombinant E. coli with BhCA-pET22b was cultivated in a medium with EDTA and lysozyme because of the efficient pelB leader sequence. rBhCA is a ∼75kDa homodimeric protein with a Tm of 72°C and T1/2 values of 66 and 24min at 50 and 60°C, respectively. SDM analysis revealed that H137, H139, H156 and H110 present in the active site play an important role in catalysis. Mineralization of CO2 using rBhCA led to the accelerated precipitation of CaCO3 in calcite form. rBhCA also functions as an efficient virtual peroxidase when Zn(2+) is substituted with Mn(2+).