Maltose and maltotriose active transport and fermentation by Saccharomyces cerevisiae

yIn the current study we analyzed the kinetics of growth, sugar consumption, and ethanol production by a Saccharomyces cerevisiae strain with the AGTI permease as its unique a-glucoside transporter on synthetic or rich medium containing maltose or maltotriose. Our results show that to efficiently consume and ferment these sugars from the medium requires constitutive expression of the transporter gene, which can be achieved by the presence of a constitutive MAL (e.g., MAL63(c)) regulator. In addition to constitutive expression of the permease, growth on rich medium also increased the fermentation performance of the cells. Although a good correlation between the activity of the AGTI transporter and the fermentation performance of the cells was observed, the same was not true for the activity of the intracellular alpha-glucosidase. The AGTI-containing S. cerevisiae strain fermented maltotriose more efficiently than maltose due to higher expression of the AGTI permease during growth on maltotriose, leading to higher uptake rates of this sugar into the cells. Our results also indicate that during maltotriose fermentation by yeasts with constitutive expression of the AGTI permease transport across the plasma membrane may no longer limit sugar utilization by S. cerevisiae cells.