This study examined how temperature affects baker's yeast (Saccharomyces cerevisiae) metabolism using continuous culture, maintaining constant growth rate while varying temperature from 25°C to 38°C. At 25°C, the yeast had a maximum growth rate of 0.22 hr⁻¹ and better glucose yield (0.225), while at 38°C growth rate increased to 0.25 hr⁻¹ but yield decreased to 0.204. At higher temperatures, ethanol production more than doubled despite identical glucose consumption, and yeast secreted significantly more pyruvate and α-ketoglutarate into the medium. Respiratory capacity declined at higher temperatures, with oxygen uptake decreasing while CO₂ output increased. Enzyme analysis revealed few differences in glycolytic or respiratory enzymes between temperatures, but α-ketoglutarate dehydrogenase activity was markedly reduced at 38°C. The NAD/NADH ratio differed between conditions (1.5 at 25°C versus 1.1 at 38°C). Cell viability and respiratory-deficient mutant frequency remained similar at both temperatures. The researchers concluded that elevated growth temperature primarily inhibits synthesis of α-ketoglutarate dehydrogenase, which secondarily promotes fermentation and reduces respiratory capacity.

Key findings

• Higher growth temperature (38°C) reduced α-ketoglutarate dehydrogenase activity and increased excretion of α-ketoglutarate and pyruvate into the medium, despite similar intracellular metabolite levels
• Ethanol production more than doubled at 38°C compared to 25°C while maintaining constant glucose utilization and growth rate in continuous culture
• Respiratory capacity declined at 38°C (lower oxygen uptake, higher CO₂ production) despite no significant changes in enzyme levels of glycolysis or most respiratory chain enzymes
• NAD/NADH ratio decreased from 1.5 at 25°C to 1.1 at 38°C, indicating more reduced cellular conditions at higher temperature
• Cell viability, respiratory-deficient mutant frequency, and mean cell dry weight were unaffected by temperature differences, suggesting effects were specific to metabolism rather than cell damage