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 degrees 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 degrees C. Even at 45 degrees 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. (C) 2014 Elsevier Ltd. All rights reserved.