Metabolic optimization of an ethanol and xylitol-coproducing Saccharomyces cerevisiae strain
Industrial Saccharomyces cerevisiae strains with excellent capacity for coproducing ethanol and xylitol from glucose and xylose are necessary for the coproduction of fuel ethanol and xylitol from lignocellulosic feedstocks such as agricultural straw.In this study,using the xylitol-producing strain CK17 as host,the effects of point mutations in the endogenous hexose transporter,elevated expression of the glycerol transporter channel Fps1p,and an increased copy number of xylose reductase-encoding genes on xylitol production were investigated using CRISPR/Cas9 gene editing technology.Point mutations in the hexose transporters Hxt3p and Hxt7p enhanced xylose consumption by 92.1％(strain CM3)and 69.0％(strain CM7),respectively.Replacing the promoter of the FPS1 gene of CM3 with the promoter of the TDH3 gene yielded strain CM3FTD,which showed a 32.6％enhancement over CM3 in its xylose consumption rate.Strain TX was obtained by increasing the copy number of the xylose reductase gene in strain CM3FTD.Its xylose consumption rate was enhanced by 17.2％over that of CM3FTD.When using pretreated straw for simultaneous saccharification and fermentation,strain TX showed significantly improved fermentation capacity compared with strain CK17,and its xylose consumption rate was enhanced by 56.4％.Cumulative xylose and ethanol reached 57.6 g/kg and 48.5 g/kg,respectively.Xylitol yield reached its theoretical maximum,and ethanol yield was 0.43 g/g-glucose.By mutating the hexose transporters and increasing Fps1p expression and xylose reductase gene copy number,S.cerevisiae strain TX with excellent ethanol-and xylitol-coproducing capacity was obtained.This strain exhibits good potential for coproduction of ethanol and xylitol from agricultural straw feedstocks.
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维普
