Enhancement of succinic acid production in Escherichia coli by metabolic engineering
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The primary goal of this project was to elucidate the production of succinic acid by two strains of Escherichia coli. Naturally occurring E. coli produces acetate, lactate, formate and small quantities of succinate. By appropriate genetic modifications, succinate can be produced as the major end product of fermentation in E. coli. In this study, the expression of the heterologous enzyme pyruvate carboxylase in E. coli is hypothesized to enhance the amount of succinate produced during the fermentation. It is also hypothesized that a novel fermentation process that commences with aerobic growth followed by anaerobic production stage would produce succinate more quickly. In order to validate the hypotheses, this project is divided into two parts. The first part (Chapter 2) was a preliminary study conducted in serum bottles and shake flasks to understand the physiological factors governing succinate production in genetically modified E. coli strains and to evaluate the rate of formation of various products. The second part (Chapter 3) employs the information obtained from the first study in fine tuning the process to gain insight into metabolic parameters such as the glucose consumption rate and carbon flow in the metabolic pathways used by E. coli in synthesizing the products under more controlled conditions.