Poster Presentation 2-34

Improvement of Xylose Reductase and Xylitol Dehydrogenase Activities from Candida guilliermondii in Sugarcane Bagasse Hydrolysate by Inoculum Cultivated in Presence of Glucose

Débora Danielle Virgínio Silva, Maria das Graças Almeida Felipe*

and Ismael Maciel Mancilha

Department of Biotechnology

Faculty of Chemical Engineering of Lorena

Lorena, SP, Brazil P. O. Box 116, 12600-970

Fax: +55 12 3153 3165

E-mail: mgafelipe@debiq.faenquil.br

Xylose reductase E.C. 1.1.1.21 (XR) and xylitol dehydrogenase E.C.1.1.1.9 (XDH) are the key enzymes responsible for the xylose-xylitol bioconversion, which is important as a biotechnological process for xylitol production from sugarcane bagasse hydrolysate. The metabolic pathway is influenced by various factors, such as the presence of glucose in hydrolysate. This hexose interferes in the xylose metabolism depending on its concentration in the fermentation medium. The effect of glucose in this metabolism was evaluated employing inoculum of Candida guilliermondii grown in synthetic medium containing as carbon source glucose (30g/L), xylose (30g/L) or mixture of glucose (2g/L) and xylose (30g/L). The fermentation medium consisted of hydrolysate (xylose: 45g/L, glucose: 1.75g/L), and the experiments were undertaken in a bioreactor (500rpm, k_La of 17h^-1, 30°C). Enzyme activities of XR and XDH were determined spectrophotometrically and the concentrations of sugars were determined by HPLC. The presence of glucose in the inoculum medium promoted an increase in 2.5 folds of XR (0.582mmol/mg_prot) and 2 folds of XDH (0.203mmol/mg_prot) activities when compared with an inoculum grown in medium containing xylose. The improvement of enzyme activities by inoculum cultivated in presence of glucose resulted in maximum values of xylitol yield (0.56g/g) and productivity (0.46g/L.h) after 48h of fermentation.