Esterases represent a group of hydrolases catalyzing the cleavage and forming of ester bonds.Many of them do not require cofactors and show wide substrate tolerance,high stereo specificity and high stability in organic solvents.These properties make esterase being attractive biocatalysts in industry.Based on genome data,we previously screened and cloned 78 esterases from six genome of the type strains belonging to family Erythrobacteraceae.One of these genes,e10(618bp)was cloned from a deep-sea bacterium Croceicoccus marinus E4A9T and over expressed in Escherichia coli Rosetta(DE3).A comparison of the amino acid sequence showed that E10could be grouped into the GDSL family.E10 was a halotolerant esterase as the optimal NaCl concentration was 3 M and was still active under 5 M NaCl.Its optimal temperature and pH were 55℃ and pH 8.0,respectively.Thermostability test showed that it maintained most of its activity for 4 h or 2 h,at 50 ℃or 60 ℃,respectively.Substrate specificity study showed E10 preferred short chain p-nitrophenylesters and exhibited maximum activity toward p-nitrophenylacetate(154.5 ± 3.9 U/mg).E10 was stable under five kinds of metal ion at a concentration of 10 mM,including Ba2+,Ca2+,Mg2+,Mn2+ and Sr2+,whereas Co2+,Cu2+,Ni2+ and Zn2+ strongly inhibited the enzyme activity.E10 was also stable in some organic solvents(15%)and detergents(1%),maintaining more than 50%of activity inacetone,acetonitrile,alcohol,DMSO,glycerol,methanol,SDS,Tween 20 and Tween 80.With its halotolerant and thermotolerant properties,E 10 is a candidate in industrial application.The crystals structure of E10 was determined at 1.66 A° resolution.Preliminary structural data revealed that E10 is a homodimer.And the C-terminals might be of great importance for the catalytic function.The structure is still under analyzing,which will provide its precise mechanisms of biocatalysis as well as thermotolerant and halotolerant properties.