Maltose and Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae (1). Sergio L. Alves-Jr, Programa de Pós-graduação Interunidades em Biotecnologia, USP-BUTANTAN-IPT, São Paulo, Brazil; Ricardo A. Herberts and Claudia Hollatz, Programa de Pós-graduação em Biotecnologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, Brazil; and Luiz C. Miletti (2) and Boris U. Stambuk (3), Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, Brazil. (1) Some of the results reported in this paper were presented at the 2005 ASBC Annual Meeting, Savannah, GA. (2) Current address: Departamento de Morfofisiologia, Centro de Ciências Agroveterinárias, Universidade do Estado de Santa Catarina, Lages, Brazil. (3) Corresponding author. E-mail: <bstambuk@mbox1.ufsc.br>; Phone: +55 48 3721-6919; Fax: +55 48 3721-9672. J. Am. Soc. Brew. Chem. 65(2):99-104, 2007.

In the current study we analyzed the kinetics of growth, sugar consumption, and ethanol production by a Saccharomyces cerevisiae strain with the AGT1 permease as its unique alpha-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 AGT1 transporter and the fermentation performance of the cells was observed, the same was not true for the activity of the intracellular alpha-glucosidase. The AGT1-containing S. cerevisiae strain fermented 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. Keywords: AGT1, Brewing, H(^+) symport, Regulation, Sugar transport