Influence of oxygen on the growth of Saccharomyces cerevisiae in continuous culture

Abstract

Baker's yeast, Saccharomyces cerevisiae, was investigated for the combined influence of dissolved oxygen and glucose concentration in continuous culture. A reactor was operated at a range of dilution rates (0.1, 0.2, 0.25, 0.27, and 3.0 h⁻¹), above and below the critical value that separates the oxidative and fermentation regions. For each dilution rate (D), steady states were established at each of five to ten different dissolved oxygen concentrations (DO) in the range of 0.01−5 mg/L. The use of on‐line mass spectrometry facilitated the measurement of gaseous and dissolved O₂, CO₂, and ethanol. Intracellular carbohydrate, protein, RNA, DNA, lipid, and cytochrome concentrations were measured. Cell size measurements were reduced to specific surface areas. Cytochrome content showed up to 100% variation during a 20‐day period of adaptation at D = 0.2 h⁻¹ to low DO. Eventually, the culture behaved the same at DO = 0.05 mg/L as it did initially at 3 mg/L. At D = 0.2, 0.25, and 0.27 h⁻¹, the transition between oxidation and fermentation was characterized by a critical DO which decreased with decreasing D. The X‐D curves were shifted such that the critical D value was reduced with decreasing DO. Specific oxygen update rates varied with DO according to the saturation kinetics. Specific cell surface areas increased with decreasing DO. Cytochrome content generally decreased with decreasing DO, and Q could be linearly related to the total cytochrome content, which exhibited a maximum at D = 0.27 h⁻¹.