Continuous succinic acid fermentation by Actinobacillus succinogenes

Abstract

Fermentations were performed in an external recycle bioreactor using CO2 and D-glucose at feed concentrations of 20 and 40 g L . 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 6.35 g L h was achieved at a dilution rate of 0.56 h . A constant succinic acid yield of 0.69±0.02 g/(g of glucose consumed) was obtained and found to be independent of the dilution rate, transient state and extent of biofilm buildup — approximately 53% 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 0.35 h when the product concentrations were low (succinic acid<10 g L ), while minimal growth was observed at succinic acid concentrations above this threshold.