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Abstract:
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In the present report we have analyzed the kinetics of growth, sugar consumption and ethanol production on synthetic or rich medium containing maltose or maltotriose by a S. cerevisiae strain with the AGT1 permease as its unique a-glucoside transporter. Our results show that in order to efficiently consume and ferment these sugars from the medium it is required constitutive expression of the transporter gene, which can be achieved by the presence of constitutive MAL (e.g. MAL63c) regulator. Besides constitutive expression of the permease, growth on rich medium also increased the fermentation performance of the cells. While a good correlation between the activity the AGT1 transporter and the fermentation performance of the cells was observed, the same was not true for the activity of the intracellular a-glucosidase. This AGT1-containing yeast strain ferments maltotriose more efficiently than maltose due to higher expression of the AGT1 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 AGT1 permease transport across the plasma membrane may no longer limit sugar utilization by S. cerevisiae cells. |
