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Response of the Energetic Metabolism of Saccharomyces cerevisiae to Different Nutritional Conditions of Carbon and Nitrogen

The energetic metabolism of Saccharomyces cerevisiae is oxidative/fermentative, and its balance can be altered by different factors such as oxygen supply and nutrient homeostasis. Carbon (C) is known as the main nutrient affecting alcoholic fermentation in S. cerevisiae, allowing fermentation as the principal pathway for energy production even in the presence of oxygen when high levels of fermentable sources are available (Crabtree effect). In addition, nitrogen (N) starvation can lead to sluggish or stuck fermentation, and the presence of certain N sources may enhance sugars consumption, associating in this way nutritional status with alcoholic fermentation. However, little is known about nutrients interactions and their effect on fermentation. The objective of this work was to investigate the impact of different C and N sources and their concentration, on the fermentative growth of S. cerevisiae. Fermentative and respiratory phenotypes of S. cerevisiae BY4742 was studied using the doubling time (Dt) to discriminate among phenotypes from 81 different conditions of N and C in duplicate, using five independent experiments. We used synthetic‐complete (SC) medium supplemented with glucose, sucrose or galactose used as C source, and proline, glutamate and ammonium as N source. Our results showed that the energetic metabolism of S. cerevisiae is directed toward fermentation or respiration depending on the type of carbon and nitrogen source and their concentrations. As expected, glucose supplementation resulted in a large number of conditions with a fermentative phenotype (19%), followed by sucrose utilization (17%). Cultures supplemented with galactose showed a fermentative phenotype only at 2% (w/v) when proline or glutamate was used as N donor (4%). The best N source was proline, irrespective of its concentration and the C source used in the culture media. Ammonium showed cellular toxicity when a concentration of 5% (w/v) was used in the cultures, and galactose supplementation showed more severe toxicity. Glutamate showed an intermediate number of fermentative phenotypes relative to proline and ammonium, despite of its quality as N donor. Our findings suggested a possible energetic role for proline that could be affecting fermentation induction.