The isomerization of xylose to xylulose is considered the most promising method for xylose utilization. The xylose isomerase (XI) gene xylA from Orpinomyces sp. ukk1 was expressed intracellularly and extracellularly in modified Saccharomyces cerevisiae strains INVSc-xylA and INVSc-SS-xylA, respectively, to enhance the synthesis of bioethanol, which is frequently utilized as a substitute for conventional fossil fuels. Moreover, the xylose transporter gene Xltr1p from Trichoderma reesei was co-expressed with xylA expressed intracellularly for INVSc-xylA-Xltr1p to further improve xylose utilization in glucose and xylose co-fermentation. INVSc-SS-xylA in mixed sugars consumed 8.30 g/L xylose, which was approximately 3- and 2-fold higher than these of INVSc-xylA and INVSc-xylA-Xltr1p, respectively. This result indicated converting xylose to xylulose prior to absorption was more effective for xylose consumption of S. cerevisiae. Furthermore, high dissolved oxygen (DO) promoted xylose utilization, regardless xylA was expressed extracellularly or intracellularly. INVSc-SS-xylA had a 1.5-fold higher xylose consumption rate than INVSc-xylA-Xltr1p. Transcriptome analysis of INVSc-SS-xylA under different DO levels indicated 967 differentially expressed genes (DEGs) were upregulated and 796 DEGs were downregulated. Most upregulated DEGs were related to TCA cycle, amino acid metabolism and energy metabolism, etc. INVSc-SS-xylA contributed to sugar-to-ethanol yield reached 0.25 g/g from pretreated bagasse hydrolysates, without detoxifying or washing pretreated biomass. These results demonstrated xylose metabolism can be improved by xylA expressed extracellularly in high DO production of ethanol from mixed sugars and provide useful methodological guidance in industrial ethanol production using undetoxified biomass.

中文翻译：

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高溶解氧下分泌表达 xylA 提高酿酒酵母木糖发酵效率


木糖异构化为木酮糖被认为是木糖利用最有前途的方法。来自Orpinomyces sp. ukk1的木糖异构酶（XI）基因xylA分别在改良酿酒酵母菌株INVSc-xylA和INVSc-SS-xylA的细胞内和细胞外表达，以增强生物乙醇的合成，生物乙醇经常被用作传统化石燃料的替代品。此外，来自里氏木霉的木糖转运蛋白基因 Xltr1p 与细胞内表达的 xylA 共表达 INVSc-xylA-Xltr1p，以进一步提高木糖在葡萄糖和木糖共发酵中的利用率。混合糖中的 INVSc-SS-xylA 消耗木糖 8.30 g/L，分别比 INVSc-xylA 和 INVSc-xylA-Xltr1p 高约 3 倍和 2 倍。这一结果表明，在吸收之前将木糖转化为木酮糖对酿酒酵母的木糖消耗更有效。此外，高溶解氧 （DO） 促进了木糖的利用，无论 xylA 是在细胞外还是细胞内表达。INVSc-SS-xylA 的木糖消耗率比 INVSc-xylA-Xltr1p 高 1.5 倍。不同 DO 水平下 INVSc-SS-xylA 的转录组分析显示，967 个差异表达基因 （DEGs） 上调，796 个 DEGs 下调。大多数上调的 DEGs 与 TCA 循环、氨基酸代谢和能量代谢等有关。INVSc-SS-xylA 导致预处理甘蔗渣水解物的糖制乙醇产量达到 0.25 g/g，无需解毒或洗涤预处理的生物质。 这些结果表明，在混合糖中乙醇的高 DO 生产中，细胞外表达的 xyylA 可以改善木糖代谢，并为使用未充气生物质的工业乙醇生产提供有用的方法指导。