Aspergillus niger has an extraordinary potential to produce organic acids as 
proven by its application in industrial citric acid production. Previously, it 
was shown that expression of the cis-aconitate decarboxylase gene (cadA) from 
Aspergillus terreus converted A. niger into an itaconic acid producer (Li et 
al., Fungal Genet Bio 48: 602-611, 2011). After some initial steps in production 
optimization in the previous research (Li et al., BMC biotechnol 12: 57, 2012), 
this research aims at modifying host strains and fermentation conditions to 
further improve itaconic acid production. Expression of two previously 
identified A. terreus genes encoding putative organic acid transporters (mttA, 
mfsA) increased itaconic acid production in an A. niger cis-aconitate 
decarboxylase expressing strain. Surprisingly, the production did not increase 
further when both transporters were expressed together. Meanwhile, oxalic acid 
was accumulated as a by-product in the culture of mfsA transformants. In order 
to further increase itaconic acid production and eliminate by-product formation, 
the non-acidifying strain D15#26 and the oxaloacetate acetylhydrolase (oahA) 
deletion strain AB 1.13 ∆oahA #76 have been analyzed for itaconic acid 
production. Whereas cadA expression in AB 1.13 ∆oahA #76 resulted in higher 
itaconic acid production than strain CAD 10.1, this was not the case in strain 
D15#26. As expected, oxalic acid production was eliminated in both strains. In a 
further attempt to increase itaconic acid levels, an improved basal citric 
acid-producing strain, N201, was used for cadA expression. A selected 
transformant (N201CAD) produced more itaconic acid than strain CAD 10.1, derived 
from A. niger strain AB1.13. Subsequently, we have focused on the influence of 
dissolved oxygen (D.O.) on itaconic acid production. Interestingly, reduced D.O. 
levels (10-25 %) increased itaconic acid production using strain N201 CAD. 
Similar results were obtained in strain AB 1.13 CAD + HBD2.5 (HBD 2.5) which 
overexpressed a fungal hemoglobin domain. Our results showed that overexpression 
of the hemoglobin domain increased itaconic acid production in A. niger at lower 
D.O. levels. Evidently, the lower levels of D.O. have a positive influence on 
itaconic acid production in A. niger strains.