The level of glucose‐6‐phosphate dehydrogenase activity strongly influences xylose fermentation and inhibitor sensitivity in recombinant Saccharomyces cerevisiae strains

Abstract
Disruption of the ZWF1 gene encoding glucose‐6‐phosphate dehydrogenase (G6PDH) has been shown to reduce the xylitol yield and the xylose consumption in the xylose‐utilizing recombinant Saccharomyces cerevisiae strain TMB3255. In the present investigation we have studied the influence of different production levels of G6PDH on xylose fermentation. We used a synthetic promoter library and the copper‐regulated CUP1 promoter to generate G6PDH‐activities between 0% and 179% of the wild‐type level. G6PDH‐activities of 1% and 6% of the wild‐type level resulted in 2.8‐ and 5.1‐fold increase in specific xylose consumption, respectively, compared with the ZWF1‐disrupted strain. Both strains exhibited decreased xylitol yields (0.13 and 0.19 g/g xylose) and enhanced ethanol yields (0.36 and 0.34 g/g xylose) compared with the control strain TMB3001 (0.29 g xylitol/g xylose, 0.31 g ethanol/g xylose). Cytoplasmic transhydrogenase (TH) from Azotobacter vinelandii has previously been shown to transfer NADPH and NAD+ into NADP+ and NADH, and TH‐overproduction resulted in lower xylitol yield and enhanced glycerol yield during xylose utilization. Strains with low G6PDH‐activity grew slower in a lignocellulose hydrolysate than the strain with wild‐type G6PDH‐activity, which suggested that the availability of intracellular NADPH correlated with tolerance towards lignocellulose‐derived inhibitors. Low G6PDH‐activity strains were also more sensitive to H2O2 than the control strain TMB3001. Copyright © 2003 John Wiley & Sons, Ltd.
Funding Information
  • Swedish National Energy Administration
  • Nordic Energy Research Programme
  • European Union (QLK3-CT-1999-51355)