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Title: Physiological consequences of triosephosphate isomerase overproduction in Saccharomyces cerevisiae
Author: Fugtong, Nantana
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Triosephosphate isomerase was overproduced in yeast Saccharomyces cerevisiae by integration of extra copies of the TPI1 gene into the yeast chromosome. Specific enzyme activity was found to have increased between 2-7 fold above the wild-type level depending on the isolate used. The physiological consequences of enzyme overproduction by a factor of 2 and 7 were studied in aerobic batch cultures and aerobic glucose-limited chemostat cultures. Batch cultivation indicated that no significant difference in growth and metabolite production between overproducers and the reference could be detected. However, lower levels of three other glycolytic enzymes (PGK, PYK and HK) were found in a 7-fold TPI overproducer. Dilution rate profiles of TPI overproducers and the reference were studied in glucose-limited chemostat culture. The 7-fold TPI overproducer showed ethanol formation at D = 0.11 h-1 where the 2-fold overproducer and the reference did not produce ethanol at all. Increase in dilution rate to 0.32 h-1 resulted in increases of ethanol production rate as well as the rates of pyruvate and acetate production. The much more sensitive competitive chemostat cultures between TPI overproducers (2-fold or 7-fold) and the reference strain were studied using LEU2 gene as a detectable marker. The marker, however, showed strong effects on selection under all competitive chemostat studies. TPI activity was therefore used as a measure to determine the proportion of the strains in competition between the reference and TPI overproducers. Results showed that the 7-fold TPI overproducer was slightly favoured when competed against the 2-fold overproducer. However, this strain was found to be inferior to the reference strain. This is discussed as a possible effect of differences in URA3 gene copy number carried in these strains.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available