Biosynthesis of Itaconic Acid

Previously, itaconic acid was isolated from pyrolytic products of citric acid or produced by converting aconitic acid present in sugar cane juice. It is now produced on a commercial basis predominantly by direct fermentation of sugars. The biosynthesis of itaconic acid follows the metabolic sequence shown in Figure 30.15. 

Fig. 30.15. Proposed metabolic sequence for biosynthesis of itaconic acid.

Genes and Enzymes Involved In the Biosynthesis of Itaconic Acid in A. terreus... 

The biosynthesis of itaconic acid is currently achieved by a submerged batch culture process using a high-producing strain of A. terreus. As substrate, typically sucrose or glucose (molasses) is used, and as second substrate oxygen is needed in order to achieve the oxidation to itaconic acid. The itaconic acid production conditions have been reviewed in more detail by Okabe, Willke, and Klement et al. [8, 32, 33] and here only the current development and the major critical... 

Bentley, R. and Thiessen, C.P. (1957) Biosynthesis of itaconic acid in Aspergillus terreus. I. Tracer studies with C14-labeled substrates. / Biol Chem., 226, 673-687. 

The biosynthesis of itaconic acid once was believed to follow the decarboxylation of aconitic acid of the citric acid cycle. Now it is thought to follow the metabolic sequence shown in Fig. 24.19. 

FIGURE 10.5 Biosynthesis of itaconic acid in the tricarboxyKc acid cycle. Modified from Willke, T., Vorlop, K.D.,... 

Fig. 15. Suggested pathway of itaconic acid biosynthesis from glucose in A. terreus [110]...

Okabe, M., Lies, D., Kanamasa, S., and Park, E.Y. (2009) Biotechnological production of itaconic acid and its biosynthesis in Aspergillus terreus. Appl. Microbiol Biotechnd., 84, 597-606. 

The biochemistry of the itaconic acid biosynthesis is very similar to that of citric acid. The general pathway from hexose to pyruvate (via the BMP pathway)... 

Expression of the Aspergillus ter-reus itaconic acid biosynthesis cluster in Aspergillus niger. Microb. Cell Eact., 13, 11. 

WinskiU, N., 1983. Tricarboxylic acid cycle activity in relation to itaconic acid biosynthesis by Aspergillus terreus. Journal of General Microbiology 129,2877-2883. www.bioconsept.eu (accessed December, 2014). 

In 1995, Bonnarme et al. [110] used the analytical techniques that combine isotopic tracing, nuclear magnetic resonance spectroscopy, and mass spectroscopy to compare the enzyme systems of intact cells of high- and low-producing strains of A. terreus. Results show that itaconate formation requires de novo protein synthesis. During acid formation, TCA cycle intermediates increase in both strains. Furthermore, data showed that both the BMP pathway and the TCA cycle are involved in itaconate biosynthesis. Based on the biosynthetic pathway (Fig. 15), one itaconate molecule is produced from one hexose molecule with a theoretical weight yield of 72.2%. The actual yield should be lower due to the loss of carbon to biomass accumulation and cell maintenance. 

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