Effects of xylulokinase activity on ethanol production from D-xylulose by recombinant Saccharomyces cerevisiae.

Aims: Recombinant Saccharomyces cerevisiae strains harbouring different levels of xylulokinase (XK) activity and effects of XK activity on utilization of xylulose were studied in batch and fed-batch cultures.
Methods and Results: The cloned xylulokinase gene (XKS1) from S. cerevisiae was expressed under the control of the glyceraldehyde 3-phosphate dehydrogenase promoter and terminator. Specific xylulose consumption rate was enhanced by the increased specific XK activity, resulting from the introduction of the XKS1 into S. cerevisiae. In batch and fed-batch cultivations, the recombinant strains resulted in twofold higher ethanol concentration and 5.3- to six-fold improvement in the ethanol production rate compared with the host strain S. cerevisiae.
Conclusions: An effective conversion of xylulose to xylulose 5-phosphate catalysed by XK in S. cerevisiae was considered to be essential for the development of an efficient and accelerated ethanol fermentation process from xylulose.
Significance and Impact of the Study: Overexpression of the XKS1 gene made xylulose fermentation process accelerated to produce ethanol through the pentose phosphate pathway.