High Gravity Ethanol Fermentations and Yeast Tolerance

Abstract

Glycogen and trehalose are two important glucose stores of the yeast Saccharomyces cerevisiae, and the content of which varies strongly and rapidly in response to changing environmental conditions. Although the metabolic pathways of these two glucose stores have been studied for decades, recent biochemical and molecular studies have unraveled unexpected metabolic features, such as the ability to accumulate glycogen in the absence of glycogenin, the demonstration that acid trehalase encoded by ATH1 is localized at the cell surface instead of the vacuole and allows cells to grow on trehalose. It is also clearly demonstrated that glycogen and trehalose pathways are subject to hierarchical control dependent on major nutrient-sensing protein kinases, namely TOR, PKA, Snf1 kinase homologous to mammalianAMP-activated protein kinase (AMPK), Pho85p, and the energy sensor Pas kinase. The sophisticated control mechanisms highlight the importance of these two glucose stores in the context of growth and cell cycle of the yeast.