title: Identification and Characterization of a Novel Salt-Tolerant Esterase from the Deep-Sea Sediment of the South China Sea.
abstract: Marine esterases play an important role in marine organic carbon degradation and cycling. Halotolerant esterases from the sea may have good potentials in industrial processes requiring high salts. Although a large number of marine esterases have been characterized, reports on halotolerant esterases are only a few. Here, a fosmid library containing 7,200 clones was constructed from a deep-sea sediment sample from the South China Sea. A geneH8encoding an esterase was identified from this library by functional screening and expressed inEscherichia coli. Phylogenetic analysis showed that H8 is a new member of family V of bacterial lipolytic enzymes. H8 could effectively hydrolyze short-chain monoesters (C4-C10), with the highest activity towardp-nitrophenyl hexanoate. The optimal temperature and pH for H8 activity were 35°C and pH 10.0, respectively. H8 had high salt tolerance, remaining stable in 4.5 M NaCl, which suggests that H8 is well adapted to the marine saline environment and that H8 may have industrial potentials. Unlike reported halophilic/halotolerant enzymes with high acidic/basic residue ratios and low pI values, H8 contains a large number of basic residues, leading to its high basic/acidic residue ratio and high predicted pI (9.09). Moreover, more than 10 homologous sequences with similar basic/acidic residue ratios and predicted pI values were found in database, suggesting that H8 and its homologs represent a new group of halotolerant esterases. We also investigated the role of basic residues in H8 halotolerance by site-directed mutation. Mutation of Arg195, Arg203 or Arg236 to acidic Glu significantly decreased the activity and/or stability of H8 under high salts, suggesting that these basic residues play a role in the salt tolerance of H8. These results shed light on marine bacterial esterases and halotolerant enzymes.
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Hao
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Yan-Qi
authors.initials: YQ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Xiu-Lan
authors.initials: XL
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Bin-Bin
authors.initials: BB
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Shi
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Bai-Cheng
authors.initials: BC
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong UniversityJinan, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and TechnologyQingdao, China.
authors.forename: Yu-Zhong
authors.initials: YZ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Institute of Marine Science and Technology, Shandong University Jinan, China.
authors.forename: Ping-Yi
authors.initials: PY
authors.lastname: Li
keywords: basic residues; deep-sea sediment; esterase; metagenomics; salt-tolerance