Teresa Cristina Zangirolami
Federal University of Goiás, Brazil
Title: Improved ethanol production from D-xylulose through evolutionary engineering of wild baker´s yeast
Biography
Biography: Teresa Cristina Zangirolami
Abstract
For enhanced economic feasibility of second generation bioethanol production, it is important to use all the fermentable fractions present in sugarcane bagasse (cellulose-C6 and hemicelluloses-C5) or other feedstocks. Xylose is the main sugar found in the C5 fraction and is not assimilated by Saccharomyces cerevisiae. However, this yeast is able to ferment D-xylulose, an isomer of xylose which can be obtained using glucose isomerase generating ethanol and xylitol as main products. This study aims to select a more suitable ethanol producer strain exhibiting lower xylitol production. Colonies isolated from industrial yeast were exposed to a sequence of evolutionary engineering procedures: Incubation on complex solid media containing xylulose (aerobic conditions); incubation of selected colonies in minimal solid medium (anaerobic conditions) and cultivation of 20 adapted colonies in cuvettes containing YNB medium and xylulose. Three colonies exhibiting lowest xylitol production were identified and characterized in terms of product formation and substrate uptake under micro aerobic conditions at 30° C. selected mutant and wild-type strains were further compared in terms of morphology and genotype. With a final ethanol concentration of 4.3 g/L for a xylitol production of 0.55 g/L, the adapted yeast showed selectivity values up to 26 mol ethanol/mol xylitol. The morphology analysis revealed that mutant strain was not able to metabolize bromocresol green dye and its colonies exhibited a darker green color on WLN agar. The results of genotypic analysis also confirmed that evolutionary engineering was able to introduce several mutations in the selected yeast.