Sucrose Fermentation by <i>Saccharomyces cerevisiae</i> Lacking Hexose Transport

Abstract

Sucrose is the major carbon source used by Saccharomyces cerevisiae during production of baker’s yeast, fuel ethanol and several distilled beverages. It is generally accepted that sucrose fermentation proceeds through extracellular hydrolysis of the sugar, mediated by the periplasmic invertase, producing glucose and fructose that are transported into the cells and metabolized. In the present work we analyzed the contribution to sucrose fermentation of a poorly characterized pathway of sucrose utilization by S. cerevisiae cells, the active transport of the sugar through the plasma membrane and its intracellular hydrolysis. A yeast strain that lacks the major hexose transporters (hxt1–hxt7 and gal2) is incapable of growing on or fermenting glucose or fructose. Our results show that this hxt-null strain is still able to ferment sucrose due to direct uptake of the sugar into the cells. Deletion of the AGT1 gene, which encodes a high-affinity sucrose-H⁺ symporter, rendered cells incapable of sucrose fermentation. Since sucrose is not an inducer of the permease, expression of the AGT1 must be constitutive in order to allow growth of the hxt-null strain on sucrose. The molecular characterization of active sucrose transport and fermentation by S. cerevisiae cells opens new opportunities to optimize yeasts for sugarcane-based industrial processes.

Impact of addition of aromatic amino acids on non-volatile and volatile compounds in lychee wine fermented with Saccharomyces cerevisiae MERIT.ferm

“…The main roles of glycerol are in the reoxidation of NADH produced by anabolic metabolism and the regulation of osmotic pressure in the presence of high sugar concentrations and other stressors such as SO 2 (Ugliano and Henschke, 2009). During the first two days of fermentation, the hydrolysis of sucrose by yeast invertase increased the concentration of fructose and glucose, which could cause osmotic pressure and rapidly increase the concentration of glycerol (Batista et al, 2005). On the other hand, some amino acids such as proline could serve as osmoprotectants, thus reducing the need for glycerol formation (Takagi, 2008).…”

Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease

“…Standard methods for yeast transformation, DNA manipulation, and analysis were employed (2). The AGT1 gene was deleted according to a previously described PCR-based gene replacement procedure (4). Briefly, the kanMX6 cassette from plasmid pFA6a-kanMX6 (26) was amplified with primers AGT1-pFA6-F1 and AGT1-pFA6-R1, and the resulting PCR product of 1,579 bp was used to transform competent yeast cells.…”

“…The molecular identity of maltotriose transporters in S. cerevisiae remained largely unknown until some years ago when a new permease gene, designated AGT1, in a partially functional mal1g locus was characterized (16). The AGT1 H ϩ symporter transports a series of ␣-glucosides (35) and has high affinity (K m , ϳ8 mM) for trehalose and sucrose and significantly lower affinity (K m , ϳ20 to 35 mM) for maltose, maltotriose, and ␣-methylglucoside (1,4,32,33). In accordance with the importance of maltotriose transport for the industrial application of yeasts, practically all brewing strains have the AGT1 permease gene in their genomes, and transcriptome studies have also shown high levels of expression of this gene during wort fermentation (19,20,23,39).…”

Construção de linhagens de Saccharomyces cerevisiae recombinantes superexpressoras de transportadores de pentoses.

“…Os genes HXT diferem entre si quanto à regulação transcricional e pós-transcricional, especificidade de substrato e afinidade por glicose (BATISTA et al, 2004;KUYPER et al, 2006). As diferenças nas cinéticas das proteínas …”