Margaret A. Harmon

Bio: Margaret A. Harmon is an academic researcher from University of Queensland. The author has contributed to research in topics: Glyoxylate cycle & Dicarboxylic acid. The author has an hindex of 1, co-authored 1 publications receiving 53 citations.

Metabolism of the anaerobic formation of succinic acid bySaccharomyces cerevisiae

Abstract: 1. Succinic acid is formed in amounts of 0.2–1.7 g/l by fermenting yeasts of the genusSaccharomyces during the exponential growth phase. No differences were observed between the various species, respiratory deficient mutants and wild type strains. 2. At low glucose concentrations the formation of succinic acid depended on the amount of sugar fermented. However, the nitrogen source was found to be of greater importance than the carbon source. 3. Of all nitrogen sources, glutamate yielded the highest amounts of succinic acid. Glutamate led to an oxidative and aspartate to a reductive formation of succinic acid. 4. A reductive formation of succinic acid by the citric acid cycle enzymes was observed with malate. This was partially inhibited by malonate. No evidence was obtained that the glyoxylate cycle is involved in succinic acid formation by yeasts. 5. Anaerobically grown cells ofSaccharomyces cerevisiae contained α-ketoglutarate dehydrogenase. Its activity was found in the 175000 x g sediment after fractionated centrifugation. The specific activity increased 6-fold after growth on glutamate as compared with cells grown on ammonium sulfate. 6. The specific activities of malate dehydrogenase, fumarase, succinate dehydrogenase, succinylcoenzymeA synthetase, α-ketoglutarate dehydrogenase and glutamate dehydrogenase (nicotinamide adenine dinucleotide dependent) were determined in yeast cells grown on glutamate or ammonium sulfate. Similar results were obtained with a wild type strain and a respiratory deficient mutant. The latter did not contain succinate dehydrogenase. 7. In fermenting yeasts succinic acid is mainly formed from glutamate by oxidation.

Removal of inhibitors of bacterial growth by dialysis culture.

Abstract: Dialysis culture was used to investigate the extent to which growth inhibition in bacterial cultures may be caused by accumulation of metabolites. Escherichia coli B was grown in a glucose/salts medium. A concentrated nutrient solution was pumped at a constant rate into the growing culture to ensure that growth was not limited by exhaustion of nutrients. In this way the only difference between growth conditions in dialysis and non-dialysis cultures was the transfer of dialysable metabolites from the culture vessel to the reservoir in the dialysis culture system. By adjusting the glucose concentration in the feed and maintaining a constant rate of feeding, glucose-limited growth could be achieved. Under these conditions, with oxygen in excess, bacterial yields of 140 to 150 g dry wt 1−1 were obtained in dialysis culture compared with 30 to 40 g 1−1 in non-dialysis culture. The high yields in dialysis culture depended on the removal of end-products of glucose metabolism. Growth inhibition was demonstrated to be the result of the combined influence of acetate, lactate, pyruvate, succinate, propionate and isobutyrate in concentrations found at the end of growth in non-dialysis cultures of Escherichia coli B.