Itaconic acid can be used as a bio-based building block for the synthesis of a large number of chemicals and polymers. Since 1950, Aspergillus terreus is used for the industrial production of itaconic acid. However, despite the long history and experience, itaconic acid production in A. terreus remains challenging and above all the required control of the morphology leads to high production costs, which causes a relatively low market volume of itaconic acid despite its chemical potential. Ustilaginaceae are promising alternative hosts that offer new possibilities to achieve more efficient itaconic aid production.          
In this thesis, Ustilago maydis and Ustilago cynodontis were applied as microbial hosts to achieve efficient itaconic acid production from glucose.        
Itaconic aid production in U. maydis and U. cynodontis was improved by metabolic engineering. The itaconic acid titer was enhanced 4.2-fold in U. maydis and 6.5-fold in U. cynodontis compared to corresponding wildtype strains.           
In order to ensure robust and non-filamentous cells growing under certain relevant conditions for itaconic acid production, the gene fuz7 was deleted in both strains. The gene fuz7 is part of the Ras/mitogen-activated protein kinase pathway and plays an important role in conjugation tube formation and filamentous growth.      
Thus, for the first time, itaconic acid production in a bioreactor with the otherwise strong filamentously growing U. cynodontis was realized. Further, by optimizing the pH value, using different feeding strategies and repeated-batch systems titer up to 83 g L^-1 could be reached in U. cynodontis.         
In U. maydis, fermentations in combination with in situ product removal using calcium carbonate precipitation resulted in a titer over 200 g L^-1 itaconic acid.        
Altogether, by an integrated approach of metabolic and morphological engineering, coupled with process development, the efficiency of itaconic acid production with U. maydis and U. cynodontis could be significantly enhanced.