Evolution of Yeast Selection for Fuel Ethanol: Breaking Paradigms
In the last 40 years, yeast selection for ethanol production has broken several paradigms such as the replacement of morphological and biochemical test for molecular tools, like electrophoretic karyotyping to monitor yeast populations, contamination by wild yeasts, and selection of dominating and persistent strains. Yeast monitoring allowed to select industrial yeast strains (PE2, CAT1, FT858L, Fermel, BG1, and SA1) that are more robust than baker’s yeast, IZ1904, and laboratory strains that were used frequently by Brazilian distilleries at that time but do not survive more than 4 weeks to successive recycles of alcoholic fermentation processes. Genomic analysis revealed that industrial yeast strains have special traits that allow industrial yeasts to adapt, survive, and dominate the fermentation in comparison with nonindustrial strains. Later, another paradigm was broken when mitochondrial DNA analysis was introduced as an additional technique to karyotyping for identification of strains derived from industrial yeasts. The combination of both methodologies allowed to select a new generation of yeast strains tailored for ethanol production. It was demonstrated that some strains are derived from selected industrial yeasts like PE2. These new strains are better adapted for each process where they arose, once that each distillery has its own fermentation conditions and very specific selection pressures are acting on the yeast population. Finally, the last paradigm broken has been the inclusion of foaming and weakly flocculating yeast strains in selection programs. In the past, these strains were excluded from selection programs because of their unwanted traits. However, it has been an additional source to select the best fitted strains and the number of tailored-yeast strains has expanded every year. These strains represent a huge opportunity to understand the mechanisms of yeast adaptation and a platform to genetic breeding for new industrial applications.
KeywordsTailored-yeast strain Process-driven selection Alcoholic fermentation Wild yeast Fuel ethanol Karyotyping, Mitochondrial DNA Saccharomyces Foaming Flocculation
Thanks to all Fermentec teams: Transfer of Technology, Engineering and New Technologies, Laboratories, Courses and Training of Staff.
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