Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology, University of Groningen, Zernike Institute for Advanced Materials and Kluyver Centre for Genomics of Industrial Fermentation, Groningen, The Netherlands.
DSM Biotechnology Center, Alexander Fleminglaan 1, 2613 AX, Delft, The Netherlands.
FEMS Yeast Res. 2021 Jan 16;21(1). doi: 10.1093/femsyr/foaa062.
Co-consumption of D-xylose and D-glucose by Saccharomyces cerevisiae is essential for cost-efficient cellulosic bioethanol production. There is a need for improved sugar conversion rates to minimize fermentation times. Previously, we have employed evolutionary engineering to enhance D-xylose transport and metabolism in the presence of D-glucose in a xylose-fermenting S. cerevisiae strain devoid of hexokinases. Re-introduction of Hxk2 in the high performance xylose-consuming strains restored D-glucose utilization during D-xylose/D-glucose co-metabolism, but at rates lower than the non-evolved strain. In the absence of D-xylose, D-glucose consumption was similar to the parental strain. The evolved strains accumulated trehalose-6-phosphate during sugar co-metabolism, and showed an increased expression of trehalose pathway genes. Upon the deletion of TSL1, trehalose-6-phosphate levels were decreased and D-glucose consumption and growth on mixed sugars was improved. The data suggest that D-glucose/D-xylose co-consumption in high-performance D-xylose consuming strains causes the glycolytic flux to saturate. Excess D-glucose is phosphorylated enters the trehalose pathway resulting in glucose recycling and energy dissipation, accumulation of trehalose-6-phosphate which inhibits the hexokinase activity, and release of trehalose into the medium.
酵母协同消耗 D-木糖和 D-葡萄糖对于高效的纤维素生物乙醇生产至关重要。需要提高糖转化率，以最小化发酵时间。先前，我们已经采用进化工程技术，在缺乏己糖激酶的木糖发酵酿酒酵母菌株中，增强 D-木糖在 D-葡萄糖存在下的转运和代谢。在高木糖消耗菌株中重新引入 Hxk2 可以在 D-木糖/D-葡萄糖共代谢过程中恢复 D-葡萄糖的利用，但速率低于非进化菌株。在没有 D-木糖的情况下，D-葡萄糖的消耗与亲本菌株相似。进化菌株在糖共代谢过程中积累了海藻糖-6-磷酸，并且海藻糖途径基因的表达增加。在 TSL1 缺失后，海藻糖-6-磷酸水平降低，混合糖上的 D-葡萄糖消耗和生长得到改善。数据表明，在高性能 D-木糖消耗菌株中，D-葡萄糖/D-木糖的共消耗会使糖酵解通量饱和。过量的 D-葡萄糖被磷酸化进入海藻糖途径，导致葡萄糖回收和能量耗散，海藻糖-6-磷酸的积累抑制己糖激酶的活性，并将海藻糖释放到培养基中。
