Construction Of The Industrial Saccharomyces Cerevisiae Strain Expressing Xylose Reductase Gene Efficiently And Primary Study On It's Xylitol Fermentation

Xylitol has attracted much attention because of its many applications in the food, medicine and chemical industries. However the use has been limited by its high price. This coast is not only a result of the consume of the activator, chemical material and energy sources, but also more difficult purification steps needed for the preparation of a pure xylose solution, which is essential for the chemical process. Fermentative production of xylitol is a promising process. The fermentative process of xylitol is an interesting alternative to conventional chemical process, since it does not require initial xylose purification. The present review describes the advantage of xylitol production by fermentation. There are many kinds of microorganism that can produce xylitol, in which yeast is the best producer of xylitol. Saccharomyces cerevisiae is recognized which is the safetiest animalcule. But it is recognized that Saccharomyces cerevisiae itself hasn't ability to metabolize xylose. The first enzymatic step in xylose metabolize was catalyzed by xylose reductase(XR), which converted xylose to xylitol. The recombinant xylitol producing S. cerevisiae was constructed by transform the XYL1 gene, which ecocding XR. The xylose metabolic pathway was established in the industrial strain of Saccharomyces cerevisiae. The recombinant strains have the ability of utilization the xylose to produce xylitol.Integratinon vector pYMIKP-XYL1 was constructed by cloning xylose reductase gene (XYL1), which originated from Pichia stipitis into multi-copy integration vertor pYMIKP. The plasmid containing XYL1 gene was transformed into the industrial strain of Saccharomyces cerevisiae 6508 and the G418 resistance gene KanMX acted as a dominant selectable marker. Further screening was performed by increasing the concentrations of G418 that provids a stronger selective pressure.and measuring the biomass following growth on YPX and another selectable marker by measuring the control wild-type clones, resulting in recombinant strains containing the XYL1 genes with mutiple copy numbers and a low copy number. The recombinant strains are named. XGHK XGH2, XGH3 and XGH5.The results of enzyme activities in YEPD...