Carbon dioxide production of wild type and PDC1 mutant Saccharomyces cerevisiae in D-glucose

Abstract

To study the differences in respiration between wild type and PDC1 mutant Saccharomyces cerevisiae, carbon dioxide (CO₂) production was observed in growth media of concentrations 0.10 M, 0.60M and 1.2 M dextrose. Respirometer measurements of the CO₂ produced were taken every five minutes for 30 minutes. The average CO₂ produced per wild type cell in 0.10 M, 0.60 M and 1.2 M was found to be 1.03 x 10^-9 mL CO₂/cell, 7.18 x 10^-10 mL CO₂/cell and 5.84 x 10^-10 mL CO₂/cell respectively, while the values of 6.59 xmL CO₂/cell, 1.27 x 10^-9 mL CO₂/cell and 9.72 x 10^-10 mL CO₂/cell were found in the mutant strain. We observed decreasing production of CO₂ in wild type and mutant cells as dextrose concentration increased from 0.6 M to 1.2 M due to the Crabtree effect. The Crabtree effect is characterized by an increase in fermentation in aerobic conditions and a decrease in respiration under excess glucose conditions. Another reason for the drop in CO₂ production from 0.6 M to 1.2 M in mutants may be due to decreased ability to breakdown pyruvate as fast as glycolysis can produce it due to the mutated pdc1 gene, which results in a pyruvate decarboxylase with impaired function. The results from our study suggest that wild-type strains may preferentially carry out fermentation in higher concentrations of glucose.  Mutants also display decreased CO₂ production; however, mutants had higher CO₂ production per cell than wild-type cells suggesting unequal repression of respiration in the two strains.