title: Characterisation of a pks gene which is expressed during ochratoxin A production by Aspergillus carbonarius.
abstract: 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.
authors.affiliation: Institute of Sciences of Food Production, ISPA-CNR, Bari, Italy. antonia.gallo@ispa.cnr.it
authors.forename: Antonia
authors.initials: A
authors.lastname: Gallo
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Perrone
authors.forename: Michele
authors.initials: M
authors.lastname: Solfrizzo
authors.forename: Filomena
authors.initials: F
authors.lastname: Epifani
authors.forename: Abdelhamid
authors.initials: A
authors.lastname: Abbas
authors.forename: Alan D W
authors.initials: AD
authors.lastname: Dobson
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Mulè
mesh_terms: D001230:Aspergillus / Q000201:enzymology* / Q000378:metabolism; D003257:Consumer Product Safety; D017931:DNA Primers; D004271:DNA, Fungal / Q000032:analysis*; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D005784:Gene Amplification; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009793:Ochratoxins / Q000096:biosynthesis*; D048630:Polyketide Synthases / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D027843:Vitis / Q000737:chemistry / Q000382:microbiology
chemical_list: D017931:DNA Primers; D004271:DNA, Fungal; D009793:Ochratoxins; C025589:ochratoxin A; D048630:Polyketide Synthases