Consolidated bioprocessing, which combines saccharolytic and fermentative abilities in a single microorganism, is receiving increased attention to decrease environmental and economic costs in lignocellulosic biorefineries. Nevertheless, the economic viability of lignocellulosic ethanol is also dependent of an efficient utilization of the hemicellulosic fraction, which contains xylose as a major component in concentrations that can reach up to 40% of the total biomass in hardwoods and agricultural residues. This major bottleneck is mainly due to the necessity of chemical/enzymatic treatments to hydrolyze hemicellulose into fermentable sugars and to the fact that xylose is not readily consumed by Saccharomyces cerevisiae—the most used organism for large-scale ethanol production. In this work, industrial S. cerevisiae strains, presenting robust traits such as thermotolerance and improved resistance to inhibitors, were evaluated as hosts for the cell-surface display of hemicellulolytic enzymes and optimized xylose assimilation, aiming at the development of whole-cell biocatalysts for consolidated bioprocessing of corn cob-derived hemicellulose. These modifications allowed the direct production of ethanol from non-detoxified hemicellulosic liquor obtained by hydrothermal pretreatment of corn cob, reaching an ethanol titer of 11.1 g/L corresponding to a yield of 0.328 g/g of potential xylose and glucose, without the need for external hydrolytic catalysts. Also, consolidated bioprocessing of pretreated corn cob was found to be more efficient for hemicellulosic ethanol production than simultaneous saccharification and fermentation with addition of commercial hemicellulases. These results show the potential of industrial S. cerevisiae strains for the design of whole-cell biocatalysts and paves the way for the development of more efficient consolidated bioprocesses for lignocellulosic biomass valorization, further decreasing environmental and economic costs.

中文翻译：

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玉米芯衍生半纤维素的综合生物加工：工程化工业酿酒酵母作为有效的全细胞生物催化剂。

在单一微生物中结合糖解和发酵能力的综合生物工艺正在受到越来越多的关注，以降低木质纤维素生物精炼厂的环境和经济成本。然而，木质纤维素乙醇的经济可行性也取决于半纤维素部分的有效利用，半纤维素部分含有木糖作为主要成分，其浓度可达到硬木和农业残余物中总生物量的 40%。这一主要瓶颈主要是由于化学/酶处理将半纤维素水解成可发酵糖的必要性，以及木糖不容易被酿酒酵母（大规模乙醇生产中最常用的生物）消耗的事实。在这项工作中，工业酿酒酵母菌株，表现出强大的特性，例如耐热性和对抑制剂的改进的抗性，被评估为半纤维素分解酶的细胞表面展示和优化木糖同化的宿主，旨在开发用于玉米芯衍生的半纤维素的综合生物加工的全细胞生物催化剂。这些改进允许从通过水热预处理玉米芯获得的未解毒半纤维素液直接生产乙醇，达到 11.1 g/L 的乙醇滴度，对应于 0.328 g/g 的潜在木糖和葡萄糖产量，而不需要外部水解催化剂。此外，发现预处理玉米芯的综合生物加工对于半纤维素乙醇生产比同时糖化和添加商业半纤维素酶的发酵更有效。