Effects of NADH-preferring xylose reductase expression on ethanol production from xylose in xylose-metabolizing recombinant Saccharomyces cerevisiae

다국어 초록 (Multilingual Abstract)

Efficient conversion of xylose to ethanol is an essential factor for commercialization of lignocellulosic ethanol. To minimize production of xylitol, a major by-product in xylose metabolism and concomitantly improve ethanol production, Saccharomyces cerevisiae D452-2 was engineered to overexpress NADH-preferable xylose reductase mutant (XR<SUP>MUT</SUP>) and NAD<SUP>+</SUP>-dependent xylitol dehydrogenase (XDH) from Pichia stipitis and endogenous xylulokinase (XK). In vitro enzyme assay confirmed the functional expression of XR<SUP>MUT</SUP>, XDH and XK in recombinant S. cerevisiae strains. The change of wild type XR to XR<SUP>MUT</SUP> along with XK overexpression led to reduction of xylitol accumulation in microaerobic culture. More modulation of the xylose metabolism including overexpression of XR<SUP>MUT</SUP> and transaldolase, and disruption of the chromosomal ALD6 gene encoding aldehyde dehydrogenase (SX6<SUP>MUT</SUP>) improved the performance of ethanol production from xylose remarkably. Finally, oxygen-limited fermentation of S. cerevisiae SX6<SUP>MUT</SUP> resulted in 0.64gl<SUP>-1</SUP>h<SUP>-1</SUP> xylose consumption rate, 0.25gl<SUP>-1</SUP>h<SUP>-1</SUP> ethanol productivity and 39% ethanol yield based on the xylose consumed, which were 1.8, 4.2 and 2.2 times higher than the corresponding values of recombinant S. cerevisiae expressing XR<SUP>MUT</SUP>, XDH and XK only.