초록
Fermentations were performed in an external recycle bioreactor using CO<SUB>2</SUB> and d-glucose at feed concentrations of 20 and 40gL<SUP>-1</SUP>. Severe biofilm formation prevented kinetic analysis of suspended cell ('chemostat') fermentation, while perlite packing enhanced the volumetric productivity by increasing the amount of immobilised cells. The highest productivity of 6.35gL<SUP>-1</SUP>h<SUP>-1</SUP> was achieved at a dilution rate of 0.56h<SUP>-1</SUP>. A constant succinic acid yield of 0.69+/-0.02g/(g of glucose consumed) was obtained and found to be independent of the dilution rate, transient state and extent of biofilm build-up - approximately 56% of the carbon that formed phosphoenolpyruvate ended up as succinate. Byproduct analysis indicated that pyruvate oxidation proceeded solely via the formate-lyase pathway. Cell growth and corresponding biofilm formation were rapid at dilution rates higher than 0.35h<SUP>-1</SUP> when the product concentrations were low (succinic acid<10gL<SUP>-1</SUP>), while minimal growth was observed at succinic acid concentrations above this threshold.