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PMID:24699234

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Citation

Gallo, A, Knox, BP, Bruno, KS, Solfrizzo, M, Baker, SE and Perrone, G (2014) Identification and characterization of the polyketide synthase involved in ochratoxin A biosynthesis in Aspergillus carbonarius. Int. J. Food Microbiol. 179C:10-17

Abstract

Ochratoxin A (OTA) is a potent mycotoxin produced by Aspergillus and Penicillium species and is a common contaminant of a wide variety of food commodities, with Aspergillus carbonarius being the main producer of OTA contamination in grapes and wine. The molecular structure of OTA comprises a dihydroisocoumarin ring linked to phenylalanine and, as shown in different producing fungal species, a polyketide synthase (PKS) is a component of the OTA biosynthetic pathway. Similar to observations in other filamentous ascomycetes, the genome sequence of A. carbonarius contains a large number of genes predicted to encode PKSs. In this work a pks gene identified within the putative OTA cluster of A. carbonarius, designated as AcOTApks, was inactivated and the resulting mutant strain was unable to produce OTA, confirming the role of AcOTApks in this biosynthetic pathway. AcOTApks protein is characteristic of the highly reduced (HR)-PKS family, and also contains a putative methyltransferase domain likely responsible for the addition of the methyl group to the OTA polyketide structure. AcOTApks is different from the ACpks protein that we previously described in A. carbonarius, which showed an expression profile compatible with OTA production. We performed phylogenetic analyses of the β-ketosynthase and acyl-transferase domains of the OTA PKSs that had been identified and characterized in different OTA producing fungal species. The phylogenetic results were similar for both domains analyzed and showed that OTA PKS of A. carbonarius, Aspergillus niger and Aspergillus ochraceus clustered in a monophyletic group with 100% bootstrap support suggesting a common origin, while the other OTA PKSs analyzed were phylogenetically distant. A quantitative RT-PCR assay monitored AcOTApks expression during fungal growth and concomitant production of OTA by A. carbonarius in synthetic grape medium. A clear correlation between the expression profile of AcOTApks and kinetics of OTA production was observed, with AcOTApks reaching its maximum level of transcription before OTA accumulation in mycelium reached its highest level, confirming the fact that gene transcription always precedes phenotypic production.

Links

PubMed Online version:10.1016/j.ijfoodmicro.2014.03.013

Keywords


Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

ASPC5:OTAA

acts_upstream_of_or_within

GO:1900818: ochratoxin A biosynthetic process

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

9EURO:G3K2A8

GO:1900818: ochratoxin A biosynthetic process

ECO:0000315:

P

Figure 3 shows that wild-type Aspergillus carbonarius produces Ochratoxin A while the mutant strain, KB1044, with a non-functioning AcOTApks gene produces no Ochratoxin A.

complete
CACAO 10054

9EURO:G3K2A8

involved_in

GO:1900818: ochratoxin A biosynthetic process

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

See also

References

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