2.5. Cloning and expression in A. niger The gene cadA which encodes cis-aconitate decarboxylase was cloned based on a PCR amplified gene copy derived from the used A. terreus strain. Two primers Cadfor53 C 50 –TCCCGGATCCTTAT ACCAGTGGCGATTT-30 , Cadrev52 C 50 -CCCCGGATCCTTATACCAGTG GCGATTTTACGG-30 containing BspHI and BamHI restriction sites, respectively, were generated to amplifying the cadA sequence based on A. terreus genomic DNA. The complete coding region of the cadA gene was isolated from the PCR product as BspHI–BamHI fragments, and cloned into the Aspergillus expression vector pAN52-4amdS. Subsequently, this vector was transformed into an Aspergillus niger strain AB 1.13. The transformants resulting for this experiment were purified twice by single colony purification on AmdS+ selection plates (Kelly and Hynes, 1985). The chromosomal DNAs were isolated from 67 h cultivated (minimal medium) A. niger AB 1.13 CAD transformants for Southern blot analysis (Okabe et al., 2009; Punt et al., 2008). Hybridisation was carried out using a probe derived from the cadA gene for probe labeling. The Alkphos direct labeling and detection system Amersham was used. As a loading control, a probe derived from the A. niger gpdA gene was used.