Simultaneous fermentation of glucose and xylose at elevated temperatures co-produces ethanol and xylitol through overexpression of a xylose-specific transporter in engineered Kluyveromyces marxianus

Engineered Kluyveromyces marxianus strains were constructed through over-expression of various transporters for simultaneous co-fermentation of glucose and xylose. The glucose was converted into ethanol, whereas xylose was converted into xylitol which has higher value than ethanol. Over-expressing xylose-specific transporter ScGAL2-N376F mutant enabled yeast to co-ferment glucose and xylose and the co-fermentation ability was obviously improved through increasing ScGAL2-N376F expression. The production of glycerol was blocked and acetate production was reduced by disrupting gene KmGPD1. The obtained K. marxianus YZJ119 utilized 120 g/L glucose and 60 g/L xylose simultaneously and produced 50.10 g/L ethanol and 55.88 g/L xylitol at 42 °C. The yield of xylitol from consumed xylose was over 98% (0.99 g/g). Through simultaneous saccharification and co-fermentation at 42 °C, YZJ119 produced a maximal concentration of 44.58 g/L ethanol and 32.03 g/L xylitol or 29.82 g/L ethanol and 31.72 g/L xylitol, respectively, from detoxified or non-detoxified diluted acid pretreated corncob.