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

Abstract: 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.