Nutrient factors specifically promoting ethanol fermentation but not growth in yeast

Yeast ethanol fermentation and growth are affected by environmental factors such as nutrients, pH, and temperature. Ethanol fermentation in yeast is typically accompanied by cell proliferation. Thus, the specific nutrients required for fermentation remain unclear. To determine nutrients required for fermentation, first a semi-synthetic medium with a small inoculum size (OD₆₀₀ = 2) was used, and CO₂ gas emissions were monitored. The addition of sodium aspartate (Asp) and MgSO₄ to a medium containing 0.2 % yeast extract and 9.1 % glucose efficiently increased gas emissions. Further addition of KH₂PO₄ and myo-inositol to the medium increased the fermentation rate. Next, to obtain no-growth conditions during fermentation, the glucose and cell amounts were increased. Cell growth was repressed but fermentation proceeded in 28.6 % glucose with a large inoculum size (OD₆₀₀ = 16 or 32). The elimination of medium components under these conditions revealed that Asp was sufficient to increase gas emissions without cell growth. Further analysis indicated that pH maintenance and aspartic acid are required to enhance fermentation under no-growth conditions.