Walfridsson M, Anderlund M, Bao X, Hahn-Hägerdal B
Department of Applied Microbiology, Lund Institute of Technology/Lund University, Sweden.
Appl Microbiol Biotechnol. 1997 Aug;48(2):218-24. doi: 10.1007/s002530051041.
Saccharomyces cerevisiae was transformed with the Pichia stipitis CBS 6054 XYL1 and XYL2 genes encoding xylose reductase (XR) and xylitol dehydrogenase (XDH) respectively. The XYL1 and XYL2 genes were placed under the control of the alcohol dehydrogenase 1 (ADH1) and phosphoglycerate kinase (PGK1) promoters in the yeast vector YEp24. Different vector constructions were made resulting in different specific activities of XR and XDH. The XR:XDH ratio (ratio of specific enzyme activities) of the transformed S. cerevisiae strains varied from 17.5 to 0.06. In order to enhance xylose utilisation in the XYL1-, XYL2-containing S. cerevisiae strains, the native genes encoding transketolase and transaldolase were also overexpressed. A strain with an XR:XDH ratio of 17.5 formed 0.82 g xylitol/g consumed xylose, whereas a strain with an XR:XDH ratio of 5.0 formed 0.58 g xylitol/g xylose. The strain with an XR:XDH ratio of 0.06, on the other hand, formed no xylitol and less glycerol and acetic acid compared with strains with the higher XR:XDH ratios. In addition, the strain with an XR:XDH ratio of 0.06 produced more ethanol than the other strains.
用分别编码木糖还原酶（XR）和木糖醇脱氢酶（XDH）的树干毕赤酵母CBS 6054的XYL1和XYL2基因转化酿酒酵母。XYL1和XYL2基因置于酵母载体YEp24中乙醇脱氢酶1（ADH1）和磷酸甘油酸激酶（PGK1）启动子的控制之下。构建了不同的载体，导致XR和XDH具有不同的比活性。转化后的酿酒酵母菌株的XR:XDH比率（比酶活性比率）在17.5至0.06之间变化。为了提高含XYL1、XYL2的酿酒酵母菌株对木糖的利用，还过表达了编码转酮醇酶和转醛醇酶的天然基因。XR:XDH比率为17.5的菌株每消耗1克木糖产生0.82克木糖醇，而XR:XDH比率为5.0的菌株每克木糖产生0.58克木糖醇。另一方面，与XR:XDH比率较高的菌株相比，XR:XDH比率为0.06的菌株不产生木糖醇，产生的甘油和乙酸较少。此外，XR:XDH比率为0.06 的菌株比其他菌株产生更多的乙醇。
