Oxygen response of the wine yeast saccharomyces cerevisiae EC1118 strain grown under carbon-sufficient, nitrogen-limited oenological conditions. http://dx.doi.org/10.1128/AEM.02305-12

Abstract

Discrete oxygen additions play a critical role in alcoholic fermentation. However, few studies have quantitated the fate of the dissolved oxygen and its impact on wine yeast cell physiology under oenological conditions. We simulated the range of dissolved oxygen concentrations that occur after a pump-over during the winemaking process, by sparging nitrogen-limited continuous cultures with oxygen-nitrogen gaseous mixtures. When the dissolved oxygen concentration increases from 1.2 to 2.7 μM, yeast cells change from a fully fermentative to a mixed respiro-fermentative metabolism. This transition is characterized by a switch in the operation of the tricarboxylic acid cycle (TCA) and an activation of NADH shuttling from the cytosol to mitochondria. Nevertheless, fermentative ethanol production remained the major cytosolic NADH sink for all oxygen conditions, suggesting the limitation of mitochondrial NADH reoxidation as the major cause of the Crabtree effect. This is reinforced by the induction of several key respiratory genes by oxygen, despite the high sugar concentration, indicating that oxygen overrides glucose repression. Genes associated with other processes such as proline uptake, cell wall remodeling and oxidative stress were also significantly affected by oxygen. The results of this study indicate that respiration is responsible for a substantial part of the oxygen response in yeast cells during alcoholic fermentation. This information will facilitate the development of temporal oxygen addition strategies to optimize yeast performance in industrial fermentations.