Screening and optimization of cholesterol conversion strain

Abstract:

Abstract:［Objective］Bacterial strain SE-1 capable of transforming cholesterol was isolated from soil and characterized．The transformation products were identified．Fermentation conditions were optimized for conversion.［Methods］Cholesterol was used as sole carbon source to isolate strain SE-1．Morphology， physiological and biochemical characteristics of strain SE-1 were studied．16S rRNA gene was sequenced and subjected to phylogenetic analysis．Fermentation supernatants were extracted with chloroform，the transformation products were analyzed by silica gel thin layer chromatography and Sephadex LH20．Their structures were identified by 1H-NMR and 13C-NMR．Fermentation medium including carbon and nitrogen，methods of adding substrates and fermentation conditions for Strain SE-1 were optimized．［Results］Strain SE-1 was a Gram-negative bacterium，exhibiting the highest homologs to Burkholderia cepacia based on the physiological analysis．The sequence analysis of 16S rＲNA gene of SE-1 strain and comparison with related Burkholderia show that SE-1 strain was very close to B．cepacia (Genbank No．U96927)．The similarity was 99%．The result of silica gel thin layer chromatography shows that strain SE-1 transformed cholesterol to two products，7β-hydroxycholesterol and the minor product was 7-oxocholesterol．The optimum culture conditions were: molasses 5%，(NH4) 2 SO4 0.3%，4% of inoculation，pH 7.5 and 36℃．Under the optimum culture condition，the conversion rate reached 34. 4% when concentration of cholesterol-Tween 80 was 1 g/L．Cholesterol 7β-hydroxylation conversion rate under optimal conditions was improved by 20.8%．［Conclusion］Strain SE-1 isolated from soil is capable of converting cholesterol at lab-scale．