Resumo

One of the main alternatives for the ethanol production from sugarcane bagasse is the enzymatic hydrolysis of lignocellulosic material, which releases fermentable sugars. The conversion of biomass to ethanol is not economically feasible unless hemicellulose is used in addition to cellulose. However, Saccharomyces cerevisiae is unable to ferment pentoses such as xylose and arabinose (released by hydrolysis of hemicellulose). Efforts have being directed to genetic engineering of S. cerevisiae with the aim of developing a strain capable of efficiently fermenting both hexose and pentose sugars to ethanol. Here, we reported the construction of a recombinant S.cerevisiae industrial strain PE-2 and evaluated its potential for using xylose both for growth and for production of ethanol. Strain PE-2 was engineered with plasmid (pRH 274) containing xyl1 and xyl2 genes from Scheffersomyces stipitis, encoding xylose reductase (XR) and xylitol dehydrogenase (XDH), respectively, and the S. cerevisiae xks1 gene encoding xylulose kinase (XK). This strain was characterized through growth assays on enriched media with increasing concentrations of xylose and determination of enzymatic activities of XR and XDH. Furthermore, a microaerophilic fermentation was performed using xylose/glucose mixtures (35g/L xylose and 15 g/L glucose) aiming to verify ethanol production. This strain showed XR and XDH activities of 0.37 and 0.051 U/mg, respectively. Through High Performance Liquid Chromatography (HPLC) analysis of the microaerophilic fermentation assay, the strain demonstrated glucose yield to ethanol of 0.49 g/g (g ethanol. g glucose comsumed-1), xylose yield to ethanol of 0.31 g/g (g ethanol. g xylose comsumed-1) and global yield of 52%, showing that this strain is more efficient at converting xylose to ethanol than native strains, like S. stipitis and Candida shehatae. The recombinant strain obtained in this work is very promising for the bioethanol production from xylose, generating perspectives for further study and possible application to industrial scale. Financial support: FAPESP and CNPq, Brazil.