A major hurdle in the production of bioethanol with second-generation feedstocks is the high cost of the enzymes for saccharification of the lignocellulosic biomass into fermentable sugars. Simultaneous saccharification and fermentation with Saccharomyces cerevisiae yeast that secretes a range of lignocellulolytic enzymes might address this problem, ideally leading to consolidated bioprocessing. However, it has been unclear how many enzymes can be secreted simultaneously and what the consequences would be on the C6 and C5 sugar fermentation performance and robustness of the second-generation yeast strain. We have successfully expressed seven secreted lignocellulolytic enzymes, namely endoglucanase, β-glucosidase, cellobiohydrolase I and II, xylanase, β-xylosidase and acetylxylan esterase, in a single second-generation industrial S. cerevisiae strain, reaching 94.5 FPU/g CDW and enabling direct conversion of lignocellulosic substrates into ethanol without preceding enzyme treatment. Neither glucose nor the engineered xylose fermentation were significantly affected by the heterologous enzyme secretion. This strain can therefore serve as a promising industrial platform strain for development of yeast cell factories that can significantly reduce the enzyme cost for saccharification of lignocellulosic feedstocks.

用第二代原料生产生物乙醇的主要障碍是用于将木质纤维素生物质糖化成可发酵糖的酶的高成本。酿酒酵母同时糖化和发酵分泌多种木质纤维素分解酶的酵母可能会解决此问题，理想情况下会导致整合的生物加工。然而，目前尚不清楚可以同时分泌多少种酶，以及对第二代酵母菌株的C6和C5糖发酵性能和稳健性有何影响。我们已经在一个第二代工业酿酒酵母中成功表达了七个分泌的木质纤维素分解酶，即内切葡聚糖酶，β-葡萄糖苷酶，纤维二糖水解酶I和II，木聚糖酶，β-木糖苷酶和乙酰木聚糖酯酶。菌株，达到94.5 FPU / g CDW，无需进行酶处理即可直接将木质纤维素底物转化为乙醇。葡萄糖和工程木糖发酵均不受异源酶分泌的影响。因此，该菌株可以用作开发酵母细胞工厂的有前途的工业平台菌株，其可以显着降低用于木质纤维素原料糖化的酶成本。