A clone-based transcriptomics approach for the identification of genes relevant for itaconic acid production in Aspergillus

A selection of 13 cDNA clones resulting in the strongest (>10-fold) differential hybridization signals were identified and subsequently the inserts of these clones were sequenced. Sequence analysis revealed the presence of in total five different gene inserts among the sequenced clones. From one of these sequences, encoding a gene of the MmgE-PrpD family, the full length coding region was shown to encode one of the crucial itaconic acid pathway enzymes cis-aconitate decarboxylase, by heterologous expression in Escherichia coli. Expression of this gene in Aspergillus niger, which is a natural citric acid producer, resulted in itaconate production. Genome analysis suggests that in A. terreus the cis-aconitate decarboxylase gene is part of an itaconate acid related gene cluster including genes encoding two pathway specific transporters and a Zinc finger protein. Interestingly, this cluster is directly linked to the large lovastatin gene cluster.