Enhancement of xylitol production in glycerol kinase disrupted Candida tropicalis by co-expression of three genes involved in glycerol metabolic pathway

Glycerol can be used as a primary carbon source by yeasts, little is known regarding glycerol metabolism in Candida tropicalis . In this study, glycerol kinase gene ( gk ) was disrupted from xylitol dehydrogenase gene (XYL2) knockout C. tropicalis strain BSXDH-3. The resultant gk knockout C. tropicalis strain was incapable to grow on glycerol. The cells growth on glycerol was resumed by co-expressing Scheffersomyces stipitis gcy1 , 2 and 3 genes, which respectively encode NADP + -dependent glycerol dehydrogenase 1, 2 and 3, under the control of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter. NADPH-dependent xylitol production was higher in the engineered strain, termed “GK”, than in BSXDH-3. In fermentation experiments using glycerol as co-substrate with xylose, strain GK produced xylitol 0.85 and 1.28 g l −1 h −1 at the time periods of 16 and 24 h, respectively, which is 30 and 18 % higher at same time intervals in BSXDH-3. This is the first report of gk gene disruption and co-expression of gcy1 , 2 and 3 genes for NADPH regeneration and enhanced xylitol production in C. tropicalis .