title: Enhancement of xylitol production in Candida tropicalis by co-expression of two genes involved in pentose phosphate pathway.
abstract: The yeast Candida tropicalis produces xylitol, a natural, low-calorie sweetener whose metabolism does not require insulin, by catalytic activity of NADPH-dependent xylose reductase. The oxidative pentose phosphate pathway (PPP) is a major basis for NADPH biosynthesis in C. tropicalis. In order to increase xylitol production rate, xylitol dehydrogenase gene (XYL2)disrupted C. tropicalis strain BSXDH-3 was engineered to co-express zwf and gnd genes which, respectively encodes glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6-PGDH), under the control of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter. NADPH-dependent xylitol production was higher in the engineered strain, termed "PP", than in BSXDH-3. In fermentation experiments using glycerol as a co-substrate with xylose, strain PP showed volumetric xylitol productivity of 1.25 g l(-1) h(-1), 21% higher than the rate (1.04 g l(-1) h(-1)) in BSXDH-3. This is the first report of increased metabolic flux toward PPP in C. tropicalis for NADPH regeneration and enhanced xylitol production.
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon, 305-701, Korea.
authors.forename: Irshad
authors.initials: I
authors.lastname: Ahmad
authors.forename: Woo Yong
authors.initials: WY
authors.lastname: Shim
authors.forename: Woo Young
authors.initials: WY
authors.lastname: Jeon
authors.forename: Byoung Hoon
authors.initials: BH
authors.lastname: Yoon
authors.forename: Jung-Hoe
authors.initials: JH
authors.lastname: Kim
mesh_terms: D041022:Candida tropicalis / Q000201:enzymology* / Q000235:genetics*; D024861:Genetic Enhancement / Q000379:methods*; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D005990:Glycerol / Q000378:metabolism*; D010734:Phosphogluconate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D014993:Xylitol / Q000096:biosynthesis* / Q000302:isolation & purification
chemical_list: D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D005990:Glycerol; D014993:Xylitol