Voll A., Klement T., Gerhards G., Buechs J., Marquardt W., 2012, Metabolic Modelling of Itaconic Acid Fermentation with Ustilago Maydis, Chemical Engineering Transactions, 27, 367-372.
Itaconic acid (IA) is considered as an important intermediate in the synthesis of bio-based chemicals and fuels. It can be produced under nitrogen-limited conditions from glucose by aerobic fermentation with the fungus Ustilago maydis (U. maydis). A metabolic model of this organism is developed to identify optimal operating conditions for a continuous fermentation which maximizes the overall itaconic acid yield. Experimental studies show that IA is only produced under nitrogen limitation. In order to capture this behaviour, the model should not only include the common metabolic pathways such as glycolysis, the pentose phosphate pathway and the tricarbonic acid cycle, but it should also comprise the amino acid metabolism as well as nucleotide and chitin synthesis. Since it has been shown experimentally that nitrogen limitation leads to changes in the elemental composition of the biomass, this effect must also be considered in the model. In this contribution, we will present a metabolic model accounting for these phenomena and compare model predictions with experimental results. A metabolic flux analysis carried out with the model clearly shows that nitrogen-free compounds such as IA acid are expressed by an overflow metabolism as soon as a nitrogen limitation occurs.
