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

Luke Gooding, Grace Lam, Simran Parmar, Jessica Sham


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.

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