Transport Proteins for Itaconic Acid Production in Aspergillus Niger

Aspergillus niger is a well-established host organism for the production of carboxylic acids. Acids like citric, gluconic and oxalic acids can already be produced by A. niger and high titers are obtained. The formation of carboxylic acids involves the shuttling of intermediate metabolites between different intracellular compartments and utilizes the different enzymatic capabilities of the respective compartment. The knowledge about the involved shuttling mechanisms and the localization of the necessary enzymes is still fragmentary.

In order to analyse the influence of the compartmentalization on the organic acid production, we have chosen itaconic acid as a target substance. Itaconic acid, which was selected by the US Department of Energy as one of the 12 building block chemicals for the industrial biotechnology, is currently produced by A. terreus. Heterologous expression of the A. terreus cadA gene also enables the formation of itaconic acid in A. niger although only low titers are obtained. An increase of the productivity was obtained by targeting the pathway to the mitochondria. Furthermore, it was shown that the heterologous expression of two transport proteins which are found in close proximity to the cadA gene in A. terreus, have a positive impact on the itaconic acid formation.

These two transport proteins are now characterized in more detail making use of an inducible promoter system. Furthermore, their localization in the cell is determined. For this purpose the proteins are tagged with GFP and analysed by fluorescence microscopy.