Gene Cloning, Expression, and Characterization of a New Carboxylesterase from Serratia sp SES-01: Comparison with Escherichia coli BioHe Enzyme

The carboxylesterase-encoding gene (bioHS) of a newly isolated strain, Serratia sp. SES-01, was cloned from the genomic DNA library by detecting formation of transparent halo around the colony on LB-tributyrin agar plates. The amino acid sequence of BioHs was highly similar to the members of the BioH enzyme family involved in the biotin biosynthetic pathway; it showed the highest similarity (91%) with that of Serratia proteamaculans. To compare BioHs with other BioH enzymes, the relatively well-known bioHe gene of E. coli was cloned with PCR. After we achieved high-level expression of soluble BioHs and BioHe through the exploration of different culture conditions, the purified BioHs and BioHe enzymes were characterized in terms of specificity, activity, and stability. BioHe was generally more robust to a change in temperature and pH and an addition of organic solvents than BioHs. The two enzymes exhibited a strong preference for carboxylesterase rather than for thioesterase and were optimal at relatively low temperatures (20-40 degrees C) and alkaline pHs, (7.5-9.0). The results in this study strongly suggested that both the BioHs and BioHe enzymes would be potential candidates for use as a carboxylesterase in many industrial applications.