Cloning, expression and characterization of a novel esterase from Bacillus pumilus

The gene encoding esterase (CE1) from Bacillus pumilus ARA with a calculated molecular weight of 28.4 kDa was cloned, sequenced and efficiently expressed in Escherichia coli. The open reading frame of 747 nucleotides encoded a protein, which was classified as a carboxylesterase with an identity of 87 % to esterase from Bacillus subtilis 168. Recombinant CE1 was purified in a single step to electrophoretic homogeneity by IMAC (Ni²⁺). The enzyme displayed maximum activity toward p-nitrophenyl (pNP) acetate at 37–40 °C and pH?6.5–7.0. It was stable in the pH range from 6.5 to 8.0, and at temperature from 25 to 40 °C. Among four p-nitrophenyl esters tested, the best substrate was pNP acetate with K _m and k _cat values of 0.33 mM and 4.07 s^?1, respectively. Amounts of 2 mM Ca²⁺ and Co²⁺ significantly increased the esterase activity to 190 and 121 %, respectively. These results suggest that CE1 has very attractive applications of increasing feed digestibility in animal nutrition in this moderate temperature range.