Department of Applied Microbiology, Lund University, PO Box 124, SE-22100 Lund, Sweden.
Biotechnol Biofuels. 2010 Jun 15;3:13. doi: 10.1186/1754-6834-3-13.
Cost-effective fermentation of lignocellulosic hydrolysate to ethanol by Saccharomyces cerevisiae requires efficient mixed sugar utilization. Notably, the rate and yield of xylose and arabinose co-fermentation to ethanol must be enhanced.
Evolutionary engineering was used to improve the simultaneous conversion of xylose and arabinose to ethanol in a recombinant industrial Saccharomyces cerevisiae strain carrying the heterologous genes for xylose and arabinose utilization pathways integrated in the genome. The evolved strain TMB3130 displayed an increased consumption rate of xylose and arabinose under aerobic and anaerobic conditions. Improved anaerobic ethanol production was achieved at the expense of xylitol and glycerol but arabinose was almost stoichiometrically converted to arabitol. Further characterization of the strain indicated that the selection pressure during prolonged continuous culture in xylose and arabinose medium resulted in the improved transport of xylose and arabinose as well as increased levels of the enzymes from the introduced fungal xylose pathway. No mutation was found in any of the genes from the pentose converting pathways.
To the best of our knowledge, this is the first report that characterizes the molecular mechanisms for improved mixed-pentose utilization obtained by evolutionary engineering of a recombinant S. cerevisiae strain. Increased transport of pentoses and increased activities of xylose converting enzymes contributed to the improved phenotype.
通过酿酒酵母高效利用木质纤维素水解液生产乙醇具有成本效益，但需要高效混合糖利用。值得注意的是，木糖和阿拉伯糖共发酵生产乙醇的速率和得率必须提高。
通过进化工程，对携带整合在基因组中的木糖和阿拉伯糖利用途径的异源基因的重组工业酿酒酵母菌株进行了改造，以提高木糖和阿拉伯糖同时转化为乙醇的能力。与出发菌株相比，进化株 TMB3130 在好氧和厌氧条件下具有更高的木糖和阿拉伯糖消耗速率。在以木糖和阿拉伯糖为唯一碳源的连续发酵过程中，通过进化获得的菌株能够以更高的产率生产乙醇，但同时伴随着木糖醇和甘油的积累，而阿拉伯糖几乎可以完全转化为阿拉伯糖醇。进一步的菌株特性分析表明，在木糖和阿拉伯糖培养基中进行长时间连续培养的选择压力导致木糖和阿拉伯糖的转运能力提高，同时还增加了来自真菌木糖途径的酶的水平。在戊糖转化途径的任何基因中都没有发现突变。
据我们所知，这是首次通过对重组酿酒酵母菌株进行进化工程来描述提高混合戊糖利用能力的分子机制的报道。戊糖转运能力的提高和木糖转化酶活性的增强有助于改善表型。
