Characterization of XtjR8: A novel esterase with phthalate-hydrolyzing activity from a metagenomic library of lotus pond sludge.

Abstract A fosmid metagenomic library containing 9.7 × 104 clones was constructed. A novel esterase, XtjR8, was isolated through functional screening. XtjR8 shared the maximum amino acid identity (44%) with acetyl-hydrolase from Streptomyces hygroscopicus, and was classified into family IV esterase. XtjR8 exhibited the highest hydrolytic activity for p-nitrophenyl acetate at 40 °C and pH 8.0, and presented more than 40% activity from 20 °C to 80 °C. More importantly, XtjR8 displayed the ability to hydrolyze both phthalate monoesters and diesters, this feature is extremely rare among previously reported esterases. Site-directed mutagenesis experiments revealed that the catalytic triad residues were Ser152, Glu246, and His276. Among them, Ser152 formed a hydrogen bond with dibutyl phthalate (DBP) by molecular docking, Gly84, Gly85, and Leu248 of conserved motifs formed hydrophobic interactions with DBP, respectively, which were important for the catalytic activity. Considering its wide range of temperature and hydrolytic potential toward phthalate esters, XtjR8 will be served as an interesting candidate for biodegradation and industrial applications.