Feasibility of xylose fermentation by engineered Saccharomyces cerevisiae overexpressing endogenous aldose reductase (GRE3), xylitol dehydrogenase (XYL2), and xylulokinase (XYL3) from Scheffersomyces stipitis

In this study, we propose an alternative strategy that employs overexpression of GRE3 coding for endogenous aldose reductase instead of XYL1 to construct efficient xylose‐fermenting S. cerevisiae. Replacement of XYL1 with GRE3 has been regarded as an undesirable approach because NADPH‐specific aldose reductase (GRE3) would aggravate redox balance with xylitol dehydrogenase (XYL2) using NAD+ exclusively. Here, we demonstrate that engineered S. cerevisiae overexpressing GRE3, XYL2, and XYL3 can ferment xylose as well as a mixture of glucose and xylose with higher ethanol yields (0.29–0.41 g g−1 sugars) and productivities (0.13–0.85 g L−1 h−1) than those (0.23–0.39 g g−1 sugars, 0.10–0.74 g L−1 h−1) of an isogenic strain overexpressing XYL1, XYL2, and XYL3 under oxygen‐limited conditions. We found that xylose fermentation efficiency of a strain overexpressing GRE3 was dramatically increased by high expression levels of XYL2. Our results suggest that optimized expression levels of GRE3, XYL2, and XYL3 could overcome redox imbalance during xylose fermentation by engineered S. cerevisiae under oxygen‐limited conditions.

Source: FEMS Yeast Research - March 4, 2013 Category: Research Authors: Soo Rin Kim, Nathania R. Kwee, Heejin Kim, Yong‐Su Jin Tags: Research Article Source Type: research