Production of Succinic Acid by E.coli from Mixtures of Glucose and Fructose

Succinic acid, derived from fermentation of renewable feedstocks, has the possibility of replacing petrochemicals as a building block chemical. Another interesting advantage with biobased succinic acid is that the production does not contribute to the accumulation of CO2 to the environment. The produced succinic acid can therefore be considered as a "green" chemical. The bacterium used in this project is a strain of Escherichia coli called AFP184 that has been metabolically engineered to produce succinic acid in large quantities from glucose during anaerobic conditions. The objective with this thesis work was to evaluate whether AFP184 can utilise fructose, both alone and in mixtures with glucose, as a carbon source for the production of succinic acid. Hydrolysis of sucrose yields a mixture of fructose and glucose in equal ratio. Sucrose is a common sugar and the hydrolysate is therefore an interesting feedstock for the production of succinic acid. Fermentations with an initial sugar concentration of 100 g/L were conducted. The sugar ratios used were 100 % fructose, 100 % glucose and a mixture with 50 % fructose and glucose, respectively. The fermentation media used was a lean, low-cost media based on corn steep liquor and a minimal addition of inorganic salts. Fermentations were performed with a 12 L bioreactor and the acid and sugar concentrations were analysed with an HPLC system. The results showed that the Escherichia coli strain AFP184 can utilise fructose both alone and in mixtures with glucose. A succinic acid concentration of 52 g/L was reached with a mixture of fructose and glucose. The corresponding mass yield was 0.71 gram succinic acid per gram anaerobically consumed sugar. It was also shown that a high initial concentration of glucose (100 g/L) did not yield high levels of acetate during fermentations with Escherichia coli strain AFP184.Validerat; 20101217 (root