Improving xylitol production at elevated temperature with engineered Kluyveromyces marxianus through over-expressing transporters

Three transporter genes including Kluyveromyces marxianus aquaglyceroporin gene (KmFPS1), Candida intermedia glucose/xylose facilitator gene (CiGXF1) or glucose/xylose symporter gene (CiGXS1) were over-expressed in K. marxianus YZJ017 to improve xylitol production at elevated temperatures. The xylitol production of YZJ074 that harbored CiGXF1 was improved to 147.62 g/L in Erlenmeyer flask at 42 °C. In fermenter, 99.29 and 149.60 g/L xylitol were produced from 99.55 and 151.91 g/L xylose with productivity of 4.14 and 3.40 g/L/h respectively at 42 °C. Even at 45 °C, YZJ074 could produce 101.30 g/L xylitol from 101.41 g/L xylose with productivity of 2.81 g/L/h. Using fed-batch fermentation through repeatedly adding non-sterilized substrate directly, YZJ074 could produce 312.05 g/L xylitol which is the highest yield reported to date. The engineered strains YZJ074 which can produce xylitol at elevated temperatures is an excellent foundation for xylitol bioconversion.