Study On Burkholderia Cepacia Conversion Of Cholesterol

Steroids play an important role in medicine, especially in steroid hormone drugs, these drugs have strong anti-infective, anti-allergic and anti-virus capabilities. They are the second largest category of drugs only lower than antibiotics. Many cholesterol derivatives are important medicinal drugs or become a key intermediate of modern pharmaceutical industry. In this paper, based on the principle of green economic, microbial transformations of cholesterol were carried out with microorganisms which could introduce active groups in active or non-activated centers of steroids in order to obtain new derivatives of potential biological activities. In this study, the main contents and results are concluded as follow:(1)Bacterial strain SE-1 isolated from soil was capable of transforming the cholesterol and characterized. Strain SE-1 was Gram-negative, which exhibited the highest levels to Burkholderia based on the conventional physiological test. The sequence analysis of 16S rRNA gene of SE-1 isolation and comparison with that of other related Burkholderia showed that SE-1 was very close to B. cepacia (Genbank No. U96927). Strain SE-1 was eventually named Burkholderia cepacia.(2)Two bioconversion products were isolated from the liquid broth of Burkholderia cepacia by Silica gel column chromatography and Sephadex LH20. The structures of them were identified by 1H-NMR,13C-NMR, DEPT1350, then determined as 7β-hydroxycholesterol(7β-HC)and 7-oxocholesterol(7-KC).(3)The Cholesterol hydroxylase was isolated and purified from the strain SE-1 by DEAE-52, SePhadexG-200 gel filtration and native gel electrophoresis.The activity of the enzyme was 37.22 U/mg. The molecular mass of the hydroxylase was about 80kDa by SDS-polyacrylamide gel electrophoresis.(4)Fermentation medium carbon, nitrogen, adding substrate ways and fermentation conditions for Strain SE-1 to product 7β-hydroxycholesterol by degrading cholesterol were optimized. The optimum culture conditions were:molasses 5%, (NH4) 2SO40.3%, 4% of inoculation, pH7.5,36℃. Under the optimum culture conditions determined, the conversion rate reached to 34.4% when the concentration of substrate cholesterol-Tween 80 was 1g/L. Cholesterol 7β-hydroxylation conversion rate under optimal conditions improved 20.8% than before optimization.