Isolamento e identificação de leveduras fermentadoras de D-xilose associadas à madeira em decomposição do Cerrado e Floresta Amazônica

Abstract

The search for alternative energy sources has been increased due to the gradual decrease of fossil fuels as well as the environmental impact caused by burning these fuels. In Brazil, sugar cane bagasse represents the main lignocellulosic waste, which has been the focus of research for the development of second generation ethanol. Sugar cane bagasse represent a promising source of cellulose and hemicelluloses, which consist of hexoses and pentoses that can be converted to ethanol by fermentation processes. Also bagasses are raw materials widely available with low cost, and already allocated in distilleries. The yeast Saccharomyces cerevisiae, used in fermentation processes, is able to ferment hexoses such as glucose, but is unable to ferment pentoses, such as xylose. According to above, new studies of yeasts able to ferment pentoses released from the hydrolysis of the hemicellulose fraction of sugar cane bagasse. The aim of the present study was the isolation, identification and characterization of yeasts associated with rotting wood able to ferment xylose ethanol. Two-hundred thirty-six yeasts isolates from 100 different rotting wood samples from two Brazilian ecosystems were obtained. In fermentation assays the reactions of peroxidase and alcohol oxidase here used to quantity ethanol. Of the 236 yeast isolates, 28 (12%) were able to produce ethanol by fermenting xylose. Among them, most ethanol producers were Cryptococcus laurentti (9 isolates), followed by Meyerozyma guilliermondii (5 isolates), Scheffersomyces stipitis (4 isolates), Asterotremella humicola (2 isolates), Cyberlindnera saturnus (2 isolates), Candida tropicalis (2 isolates) and Rhodotorula mucilaginosa (1 isolate). Two possible new species were found in this study, identified as Candida and Geotrichum. The results of this study indicate the importance of the biotechnological potential from Brazilian ecosystems of yeasts to be use in applications such as the production of bioethanol from lignocellulosic biomass.