Characterisation of a pks gene which is expressed during ochratoxin A production by Aspergillus carbonarius

• Published in: International journal of food microbiology 2009-01, Vol.129 (1), p.8-15
• Main Authors: Gallo, Antonia, Perrone, Giancarlo, Solfrizzo, Michele, Epifani, Filomena, Abbas, Abdelhamid, Dobson, Alan D.W., Mulè, Giuseppina
• Format: Article
• Language: English
• Subjects: Aspergillus - enzymology; Aspergillus - metabolism; Aspergillus carbonarius; Biological and medical sciences; biosynthesis; Consumer Product Safety; culture media; DNA Primers; DNA, Fungal - analysis; Food Contamination - analysis; Food industries; Food Microbiology; food pathogens; Food toxicology; Fundamental and applied biological sciences. Psychology; Gene Amplification; Gene expression; genes; Grapes; Hydrogen-Ion Concentration; Molecular Sequence Data; Ochratoxin A; Ochratoxins - biosynthesis; Penicillium; Polyketide synthase genes; polyketide synthase genes (pk); Polyketide Synthases - genetics; polyketides; Polymerase Chain Reaction - methods; secondary metabolites; Sequence Alignment; Sequence Analysis, DNA; Sequence Analysis, Protein; synthetic products; toxigenic strains; virulence; Vitaceae; Vitis - chemistry; Vitis - microbiology
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2008.10.022

Aspergillus carbonarius is considered the main fungus responsible for ochratoxin A (OTA) contamination in grapes. OTA is a potent nephrotoxin and a possible human carcinogen with a polyketide derived structure. Fungal polyketide synthases (PKSs) have recently been demonstrated to be involved in OTA biosynthesis in both Penicillium and Aspergillus species. We report here on the identification and characterisation of part of a novel polyketide synthase gene, ACpks from A. carbonarius. The sequence appears to encode conserved ketosynthase and acyl transferase domains, which are characteristic of previously characterised PKS enzymes. Expression of the ACpks gene is differentially regulated, with transcription being observed when the fungus was grown on synthetic grape medium and on OTA permissive medium (MM) whereas no transcription was detected when the fungus was grown on OTA restrictive medium (YES). ACpks expression was also observed when A. carbonarius was grown at low pH, with concomitant increases in OTA production. This correlation between ACpks gene expression and OTA production suggests the likely involvement for the product of this gene in ochratoxin A biosynthesis in the fungus. From a preliminary screening of Aspergillus isolates with ACpks specific primers, ACpks gene homologues appear to be present in A. sclerotioniger and A. ibericus, two species of section Nigri which are closely related to A. carbonarius.