Abstract:
Increased pentose phosphate pathway flux, relative to total substrate uptake flux, is shown to
enhance succinic acid (SA) yields under continuous, non-growth conditions of Actinobacillus
succinogenes biofilms. Separate fermentations of glucose and xylose were conducted in a
custom, continuous biofilm reactor at four different dilution rates. Glucose-6-phosphate
dehydrogenase assays were performed on cell extracts derived from in situ removal of
biofilm at each steady-state. The results of the assays were coupled to a kinetic model that
revealed an increase in oxidative pentose phosphate pathway (OPPP) flux relative to total
substrate flux with increasing SA titre, for both substrates. Furthermore, applying metabolite concentration data to metabolic flux models that include the OPPP, revealed similar flux
relationships to those observed in the experimental kinetic analysis. A relative increase in
OPPP flux produces additional reduction power that enables increased flux through the
reductive branch of the TCA cycle, leading to increased SA yields, reduced by-product
formation and complete closure of the overall redox balance.
