Department of Food Science and Human Nutrition, University of Illinois, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 2011 Jan 11;108(2):504-9. doi: 10.1073/pnas.1010456108. Epub 2010 Dec 27.
The use of plant biomass for biofuel production will require efficient utilization of the sugars in lignocellulose, primarily glucose and xylose. However, strains of Saccharomyces cerevisiae presently used in bioethanol production ferment glucose but not xylose. Yeasts engineered to ferment xylose do so slowly, and cannot utilize xylose until glucose is completely consumed. To overcome these bottlenecks, we engineered yeasts to coferment mixtures of xylose and cellobiose. In these yeast strains, hydrolysis of cellobiose takes place inside yeast cells through the action of an intracellular β-glucosidase following import by a high-affinity cellodextrin transporter. Intracellular hydrolysis of cellobiose minimizes glucose repression of xylose fermentation allowing coconsumption of cellobiose and xylose. The resulting yeast strains, cofermented cellobiose and xylose simultaneously and exhibited improved ethanol yield when compared to fermentation with either cellobiose or xylose as sole carbon sources. We also observed improved yields and productivities from cofermentation experiments performed with simulated cellulosic hydrolyzates, suggesting this is a promising cofermentation strategy for cellulosic biofuel production. The successful integration of cellobiose and xylose fermentation pathways in yeast is a critical step towards enabling economic biofuel production.
用于生物燃料生产的植物生物质将需要有效地利用木质纤维素中的糖，主要是葡萄糖和木糖。然而，目前用于生物乙醇生产的酿酒酵母菌株发酵葡萄糖但不发酵木糖。经过工程改造以发酵木糖的酵母发酵速度较慢，并且在葡萄糖完全消耗之前不能利用木糖。为了克服这些瓶颈，我们设计了酵母以共发酵木糖和纤维二糖的混合物。在这些酵母菌株中，通过高亲和力纤维二糖转运蛋白的导入，细胞内β-葡聚糖酶的作用在酵母细胞内发生纤维二糖的水解。细胞内水解纤维二糖可最大程度地减少葡萄糖对木糖发酵的抑制作用，从而允许纤维二糖和木糖的共消耗。与单独以纤维二糖或木糖作为唯一碳源进行发酵相比，产生的酵母菌株同时共发酵纤维二糖和木糖，并且表现出提高的乙醇产率。我们还观察到，在用模拟纤维素水解物进行的共发酵实验中，产量和生产率得到了提高，这表明这是一种有前途的纤维素生物燃料生产的共发酵策略。在酵母中成功整合纤维二糖和木糖发酵途径是实现经济生物燃料生产的关键步骤。
