Leveduras fermentadoras de celobiose isoladas de ecossistemas brasileiros

Abstract

The fossil fuels restriction and new policies of sustainable development have been increased the demand for alternative fuels and in this scenario the secondgeneration ethanol became a priority. The cellulose hydrolysis is a critical step in the process, since the enzymes are inhibited by products, glucose and cellobiose. Cellobiose-fermenting yeasts is an interesting alternative and applying them could increase the ethanol yield, by metabolizing cellobiose in addition to glucose. The goals of this study were to isolate, identify and characterize cellobiose-fermenting yeast and identify genes of cellobiose metabolism. A total of 647 yeasts strains were isolated and 133 species were identified, where 48 are new species for science. Candida boidinii was found more frequently. Scheffersomyces queiroziae, Sc. amazonensis, Yamadazyma cellobiosica sp. nov., C. jaroonii, C. tammaniensis, and Hanseniaspora opuntiae produced more ethanol and were selected to characterize the fermentative metabolism of cellobiose. The yeasts showed intracellular β- glucosidase activity and high ethanol yields and fermentation efficiency, Sc. ueiroziae and Sc. amazonensis showed the best profiles. The genome of Sc. queiroziae was sequenced and 9 hypothetical genes were found, encoding sugar transporters and β-glucosidases enzymes. Two genes similar to Sc. stipitis genes HXT2.4 and BGL5 have been expressed in Saccharomyces cerevisiae. The recombinant strains showed intracellular β-glucosidase activity and could ferment cellobiose with 50% efficiency. The results show the biotechnological potential of yeasts isolated from Brazilian biodiversity for use in fermentation processes and to obtain new interesting genes for future studies in lignocellulosic ethanol production.