Characterization of a novel carboxylesterase from Bacillus velezensis SYBC H47 and its application in degradation of phthalate esters

Abstract

Recently, residual plasticizer phthalate esters (PAEs) in the different environments pose a serious health threat to humans and mammals. Biodegradation has been considered a promising and eco-friendly way to eliminate PAEs. In this study, a gene (baces04) encoding the novel PAEs hydrolase, carboxylesterase (BaCEs04), was screened from the genome of Bacillus velezensis SYBC H47 via bioinformatics analysis. Then, baces04 was cloned and expressed in Escherichia coli BL21 (DE3). BaCEs04 belonged to the esterase family VI. It contained a conserved domain (Gly₁₅₉-His₁₆₀-Ser₁₆₁-Leu₁₆₂-Gly₁₆₃) and a typical serine hydrolase catalytic site (Ser₁₆₁-Asp₂₀₄-His₂₆₁). The characterization of BaCEs04 showed that the activity was optimal at 60°C and pH 7.5. This enzyme also displayed high resistance to metal ions, organic solvents, and detergents. After treatment with BaCEs04 for 5 h, the degradation ratio of four different 1 mM PAEs, including dimethyl phthalate, diethyl phthalate, dipropyl phthalate, and dibutyl phthalate, was 32.4%, 50.5%, 77.9%, and 86.8%, respectively. The degradation products of four PAEs were identified as their corresponding monoalkyl phthalates. This is the first report that family VI esterase displaying PAE-hydrolysis activity. This study also proved that BaCEs04 could be used as an ideal candidate for the application in bioremediation and industry.

Keywords: Bacillus velezensis; Bioinformatics analysis; Carboxylesterase; Esterase family VI; Phthalate esters.