Improving co-fermentation of glucose and xylose by adaptive evolution of engineering xylose-fermenting Saccharomyces cerevisiae and different fermentation strategies

Xylose utilization of engineered yeast is vulnerable to inhibitors generated during pretreatment of lignocellulose. In this study, adaptive evolution was applied to enhance the tolerance of xylose-fermenting strain. Compared to the parental strain, the ethanol yield was increased by 60% and 80% for the adapted strain (E7-403) when xylose was used as the sole carbon resource with 20% and 50% inhibitor cocktails, respectively. E7-403 removed furfural more effectively than parental strain (E7) in the fermentation with 100% inhibitor cocktails. In the fermentation with mixed sugar and high inhibitor concentration, glucose was depleted within 36 h for E7-403 while 6.1 glucose was still left after 120 h for E7. Consequently, ethanol yield of E7-403 was 22.9% higher than that of E7. It was demonstrated that E7-403 strain exhibited an enhanced ability for regulating cellular reactive oxygen species, which alleviated the harmful effects of inhibitors. Meanwhile, E7-403 strain was further applied in co-culture and pre-fermentation process to improve xylose utilization. (C) 2019 Elsevier Ltd. All rights reserved.