Nitrogen and redox metabolism in Saccharomyces cerevisiae - Impact on cellular activity and ethanol production.
Ethanol production by yeast fermentation has been in focus of mankind for millennia, initially, as consumable products like wine and beer, and recently as an environmental-friendly fuel. To obtain an efficient industrial production further knowledge of yeast metabolism is needed to increase the product purity. In this work, the nitrogen and redox metabolism in yeast and its implications on by-product formation and yeast physiology have been studied. In this respect, amino acid biosynthesis plays a substantial role and the central amino acid, glutamate, where used as the sole source of nitrogen. Such cultures were studied in depth by characterizing extra- and intracellular metabolite formation, carbon flows, protein expression and enzyme activities. Glycerol is formed as the main by-product during anaerobic conditions to balance redox equivalents formed during biosynthesis of mainly amino acids. Thus, using amino acids as nitrogen source it was found that glycerol formation was reduced as predicted by theoretical calculations. The results presented in this work have implications for both basic yeast research as well as development of yeast bioprocesses.