Effects of overexpression of acetaldehyde dehydrogenase 6 and acetyl-CoA synthetase 1 on xylitol production in recombinant Saccharomyces cerevisiae

Supply of NAD(P)H is a key factor in microbial production of xylitol from xylose. To facilitate NAD(P)H supplementation, acetaldehyde dehydrogenase 6 (ALD6) and acetyl-CoA synthetase 1 (ACS1) were overexpressed in recombinant Saccharomyces cerevisiae harboring the Pichia stipitis xylose reductase (XR) gene. In-vitro activity analysis confirmed the functional expression of both enzymes. Glucose-limited fed-batch fermentations of Saccharomyces cerevisiae BJ3505:δXR strains overexpressing ACS1 and/or ALD6 were performed by feeding 600 g/L glucose in the presence of 100 g/L xylose. Among them, ACS1 overexpression gave the best result of xylitol production: 91.3 g/L xylitol concentration and 1.76 g/L h xylitol productivity, which were 25% and 11% increase, relative to those of the control and ALD6-overexpressing strains. Considering the changes of cell growth, ethanol and acetate production, a remarkable enhancement of xylitol production by ACS1 overexpression seemed be ascribed to energy and NAD(P)H generation through a metabolism from acetaldehyde to acetyl-CoA and TCA cycle.