Monday, July 25, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Genetically engineered Saccharomyces cerevisiae has been developed to improve the capacity for converting xylose into ethanol. Numerous studies have indicated that efficient utilization of xylose by recombinant S. cerevisiae was directly involved with the specific cofactor usage and the ratio of enzymes activities in metabolic pathway. This study was aimed to describe a way to enhance the ethanol yield and xylose consumption rate for recombinant S. cerevisiae. A previously constructed recombinant S. cerevisiae YY2KL, which was able to express NADPH-dependent xylose reductase(XR), NAD+-dependent xylitol dehydrogenase(XDH) and xylulose kinase(XK) has showed the capacity of xylose utilization with a low ethanol yield and xylose consumption rate. Consequently, recombinant expression plasmid contained XR gene was transformed and integrated into aur1 site of YY2KL. Two recombinant expression plasmids contained NADP+-dependent XDH mutant and XK genes were dually transformed and integrated into 5S rDNA site of YY2KL. This systematic method could built the S. cerevisiae library with different ratios of xylose metabolic genes, and well-growth colonies with different fermentation capacities for xylose was further selected by YEPX(1% yeast extract, 2% peptone, 2% xylose). We successfully isolated a recombinant strain with an attractive capacity for xylose fermentation, and then designated it as strain YY5A. The specific xylose consumption rate by strain YY5A was estimated to be 0.54 g/gDW/h, which was increased 1.64 times compared to 0.33 g/gDW/h by the parent strain YY2KL. The ethanol yield was also enhanced 2.08 times by this novel method.