Zhang Jinliang, Li Sha, Xu Hong, Zhou Peng, Zhang Lujia, Ouyang Pingkai
State Key Laboratory of Materials-Oriented Chemical Engineering, ‡College of Food Science and Light Industry, and §College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology , Nanjing 210009, P. R. China.
J Agric Food Chem. 2013 Mar 20;61(11):2861-7. doi: 10.1021/jf304983d. Epub 2013 Mar 6.
Gluconobacter oxydans is known to be a suitable candidate for producing xylitol from d-arabitol. In this study, the enzyme responsible for reducing d-xylulose to xylitol was purified from G. oxydans NH-10 and characterized as xylitol dehydrogenase. It has been reported that XDH depends exclusively on NAD(+)/NADH as cofactors with a relatively low activity, which was proposed to be the direct reason for its limiting the overall conversion process. To better produce xylitol, an engineered G. oxydans PXPG was constructed to coexpress the XDH gene and a cofactor regeneration enzyme (glucose dehydrogenase) gene from Bacillus subtilis. Activities for both enzymes were more than twofold higher in the G. oxydans PXPG than in the wild strain. Approximately 12.23 g/L xylitol was obtained from 30 g/L d-arabitol by resting cells of the engineered strain with a conversion yield of 40.8%, whereas only 7.56 g/L xylitol was produced by the wild strain with a yield of 25.2%. These results demonstrated that increasing the XDH activity and the cofactor NADH supply could improve the xylitol productivity notably.
氧化葡萄糖杆菌被认为是从D-阿拉伯糖醇生产木糖醇的合适候选菌株。在本研究中，从氧化葡萄糖杆菌NH-10中纯化出负责将D-木酮糖还原为木糖醇的酶，并将其鉴定为木糖醇脱氢酶。据报道，木糖醇脱氢酶仅依赖NAD(+)/NADH作为辅因子，活性相对较低，这被认为是其限制整体转化过程的直接原因。为了更好地生产木糖醇，构建了工程菌氧化葡萄糖杆菌PXPG，使其共表达木糖醇脱氢酶基因和来自枯草芽孢杆菌的辅因子再生酶（葡萄糖脱氢酶）基因。氧化葡萄糖杆菌PXPG中这两种酶的活性均比野生菌株高出两倍以上。利用工程菌的静息细胞从30 g/L D-阿拉伯糖醇中获得了约12.23 g/L木糖醇，转化率为40.8%，而野生菌株仅产生了7.56 g/L木糖醇，产率为25.2%。这些结果表明，提高木糖醇脱氢酶活性和辅因子NADH的供应可以显著提高木糖醇的生产效率。
