Screening Of Sterol Esterase-producing Strain And Study On Its Enzymatic Properties

Sterol esterase also named cholesterol esterase（E.C3.1.1.13）. It can hydrolyze sterol ester tobe sterol and fatty acid. Sterol esterase associated with cholesterol oxidase was used to detect thetotal amount of cholesterol in blood. Recent years, the application area of sterol esterase wasbroaden gradually. Some reports showed that sterol esterase of Ophiostoma piceae andMelanocarpus albomyces had the potential to solve the pitch problems caused by lipophilicextractives during mechnical pulping of wood. At the present time, the source of sterol esteraaseis limite, and the activity of sterol esterase is low. There is a long way to apply the enzyme inpractice. More sterol esterase need to be studied.Twenty four strains producing sterol esterase were screened from soil by using a plate assayin a medium containing sterol ester and fluorescent dye rhodamine B. Among these strains, jx-39,which was found to produce the highest level of sterol esterase and belongs to gennusChryseobacterium based on16S rDNA sequencing analysis, then was designated asChryseobacterium sp.jx-39.The enzyme activity of Chryseobacterium sp.jx-39reached0.194IU/mL after18hoursinduction under the optimized culture conditions（0.2%vegetable oil,0.5%beef extract,0.2%K₂HPO₄,0.05%MgSO₄·7H₂O,0.1%（NH₄）₂SO₄,1%glucose, pH7.0;10%broth content,2%inoculation amount, temperature30oC, rotation sp.eed200rpm）.The sterol esterase was partially purified by ion exchange chromatography on DEAESepharose Fast Flow column. This enzyme showed an optimum activity at pH of7.5andtemperature of40oC. The enzyme had good thermostability below45oC and pH stability at5.0-9.0. Chryseobacterium sp.jx-39sterol esterase can hydrolyze cholesterol esters and pNP esters ofdifferent fatty acids. It may have the potential to solve the pitch problems caused by lipophilicextractives during mechnical pulping of wood.