Xylitol production by genetically modified industrial strain of Saccharomyces cerevisiae using glycerol as co-substrate.

Xylitol is commercially used in chewing gum and dental care products as a low calorie sweetener having medicinal properties. Industrial yeast strain of S. cerevisiae was genetically modified to overexpress an endogenous aldose reductase gene GRE3 and a xylose transporter gene SUT1 for the production of xylitol. The recombinant strain (XP-RTK) carried the expression cassettes of both the genes and the G418 resistance marker cassette KanMX integrated into the genome of S. cerevisiae. Short segments from the 5' and 3' delta regions of the Ty1 retrotransposons were used as homology regions for integration of the cassettes. Xylitol production by the industrial recombinant strain was evaluated using hemicellulosic hydrolysate of the corn cob with glucose as the cosubstrate. The recombinant strain XP-RTK showed significantly higher xylitol productivity (212 mg L-1 h-1) over the control strain XP (81 mg L-1 h-1). Glucose was successfully replaced by glycerol as a co-substrate for xylitol production by S. cerevisiae. Strain XP-RTK showed the highest xylitol productivity of 318.6 mg L-1 h-1 and titre of 47 g L-1 of xylitol at 12 g L-1 initial DCW using glycerol as cosubstrate. The amount of glycerol consumed per amount of xylitol produced (0.47 mol mol-1) was significantly lower than glucose (23.7 mol mol-1). Fermentation strategies such as cell recycle and use of the industrial nitrogen sources were demonstrated using hemicellulosic hydrolysate for xylitol production.