Comparative Genomic Analysis and Phenotypic Characterization of <em>Saccharomyces cerevisiae</em> Strains used in Sugarcane-based Fermentation Processes to Improve Sucrose Fermentation by an Industrial Fuel-ethanol Yeast Strain

Abstract

In Brazil, sucrose-rich broths (cane juice and/or molasses) are used to produce billions of liters of both fuel ethanol and cacha&amp;ccedil;a per year using selected Saccharomyces cerevisiae industrial strains. Aiming to improve this disaccharide fermentation, we have first determined the genetic characteristics, by array comparative genomic hybridization, of a group of 8 fuel ethanol and 5 cacha&amp;ccedil;a industrial yeasts that tend to dominate the fermentors during the production season. The widespread presence of SUC genes encoding invertase at multiple telomeres has been shown to be a common feature of both baker&amp;rsquo;s and distillers&amp;rsquo; yeast strains and is postulated to be an adaptation to sucrose-rich broths. Our results show that only two strains (one fuel ethanol and one cacha&amp;ccedil;a yeast) have amplification of the SUC genes, with high invertase activity. The other industrial yeast strains had a single SUC locus (SUC2) in their genome, with different patterns of invertase activity. These results indicate that invertase activity probably does not limit sucrose fermentation during fuel ethanol and cacha&amp;ccedil;a production by these industrial strains. Using this knowledge, we changed the mode of sucrose metabolism of an industrial strain by avoiding extracellular invertase activity, overexpressing the intracellular invertase, and increasing its transport through the AGT1 permease. This approach allowed higher ethanol production from sucrose by the modified industrial yeast when compared to its parental strain.