Molecular strategy to discriminate between two ochratoxin A producing Aspergillus niger aggregate species isolated from fresh and dried grapes.

Aspergillus genus is an ubiquitous fungal group that colonizes a wide range of substrates. A total of 100 Tunisian fungal strains isolated at harvest time from fresh and dried grapes were identified within the section Nigri and tested for their ochratoxin A (OTA) producing abilities. Of the isolates, 45% were identified as Aspergillus tubingensis, 34% as Aspergillus niger, 12% as Aspergillus japonicus and 9% as Aspergillus carbonarius. The OTA production was assessed using Czapeck yeast extract agar which revealed that 25% of the isolates belonging to the Aspergillus niger aggregate were OTA producers, while 97% were identified as belonging to the A. Carbonarius species. To distinguish between A. Niger and A. Tubingensis, PCR was used to amplify the ITS-5.8S rDNA for these two strains. The sequence analysis of the PCR products revealed a full similarity between the two species. Thus, a new molecular strategy has been developed based on the targeting of the gene from nitrate reductase ( niiA) and nitrite reductase gene ( niaD), as well as the intergenic region of the gene ( niiA-niaD). The subsequent screening revealed that two new specific primer pairs can be used to identify specifically A. Niger and A. Tubingensis. [ABSTRACT FROM AUTHOR]