Zhang Lingyan, Zhang Liang, Ding Zhongyang, Wang Zhengxiang, Shi Guiyang
Key Laboratory of Industrial Biotechnology of Ministry of Education, Jiangnan University, Wuxi 214122, China.
Sheng Wu Gong Cheng Xue Bao. 2008 Jun;24(6):950-6.
One yeast strain, which was isolated from 256 natural samples, was found to be able to utilize D-xylose effectively. On the basis of assimilation physiological and molecular biological tests, the yeast strain was identified as a strain of Candida tropicalis. Furthermore, metabolic engineering breeding strategy was applied to change the metabolic flux in order to increase ethanol productivity. In this study, the C. tropicalis was used as the host strain and the plasmid pYX212-XYL2, which was formerly constructed for over expression of XYL2 gene encoding xylitol dehydrogenase (XDH) from Pichia stipitis, was used as the backbone of the recombinant vector. A hygro gene was inserted into downstream position of XYL2 gene, meanwhile, the result plasmid pXY212-XYL2-Hygro transformed into C. tropicalis by electroporation. Thus, a recombinant yeast C. tropicalis XYL2-7 was obtained through hygromycin B resistance screening and its specific XDH activity was 0.5 u/mg protein, which was 3 times more than that of the parent strain. Additionally, the recombinant yeast was applied in the fermentation of xylose. Compared with the parent yeast, it was concluded that the xylitol yield in the broth decreased by 3 times, however, the ethanol yield increased by 5 times. The feasibility of ethanol production from xylose by C. tropicalis was firstly studied in this paper. These research results are helpful to advance the bioconversion of renewable resources (e. g. straw, wheat bran, and husk) to fuel ethanol.
从256个天然样品中分离出的一株酵母菌株被发现能够有效利用D-木糖。基于同化生理和分子生物学测试，该酵母菌株被鉴定为热带假丝酵母菌株。此外，应用代谢工程育种策略来改变代谢通量以提高乙醇生产率。在本研究中，热带假丝酵母用作宿主菌株，先前构建用于过表达来自树干毕赤酵母的编码木糖醇脱氢酶（XDH）的XYL2基因的质粒pYX212-XYL2用作重组载体的骨架。将潮霉素基因插入XYL2基因的下游位置，同时，通过电穿孔将所得质粒pXY212-XYL2-Hygro转化到热带假丝酵母中。通过潮霉素B抗性筛选获得重组酵母热带假丝酵母XYL2-7，其比XDH活性为0.5 u/mg蛋白，是亲本菌株的3倍。此外，将重组酵母应用于木糖发酵。与亲本酵母相比，得出肉汤中木糖醇产量降低了3倍，然而乙醇产量增加了5倍的结论。本文首次研究了热带假丝酵母由木糖生产乙醇的可行性。这些研究结果有助于推动可再生资源（如秸秆、麦麸和稻壳）向燃料乙醇的生物转化。
