Comparison of fermentation rates of a wild-type and YRL044C mutant strain of Saccharomyces cerevisiae by ethanol production quantification

Abstract

Saccharomyces cerevisiae (also known as brewer’s yeast) undergoes alcoholic fermentation as a form of metabolism, which is facilitated by pyruvate decarboxylase.  The PDC1 gene is one of three genes that can encode this isoenzyme, and in this experiment, we investigated the difference in fermentation rates of wild-type BY4741A S. cerevisiae versus a PDC1-deficient YRL044C variant. To calculate these rates, we used a by-product, ethanol, as an indicator of fermentation. Ethanol concentration was calculated from the specific gravity measurement.  Equal initial numbers of wild-type and mutant cells were cultivated in a YPD broth for growth and incubated at 32°C in anaerobic conditions to promote growth and fermentation. Over a span of 10 days, we observed a greater slope in ethanol concentration per yeast cell in wild-type S. cerevisiae. The slope represents the increase of ethanol concentration of each cell per day, and it was calculated to be 4x10^-6 for the wild-type and 2x10^-6 for the mutant (% per cell per day). Through a two-way ANOVA, our results showed a significant difference between the ethanol production by the two strains. However, a significant difference between the two strains was not found in the pattern of ethanol production over time.