Abstracts (WP6) pag. 4

The biosynthesis of ochratoxin A by Penicillium as one mechanism for adaptation to NaCl rich foods

Penicillium nordicum is an ochratoxin A producing filamentous fungus, which is adapted to sodium
chloride and protein rich food environments like certain cheeses or dry cured meats. Penicillium verrucosum
usually occurs on cereals but can also be isolated from brined olives. It could be shown that
sodium chloride has a profound influence on the regulation of ochratoxin A biosynthesis in both Penicillium
species. High amounts of ochratoxin A are produced by P. nordicum over a wide concentration
range of NaCl (5e100 g/l) with a weak optimum at about 20 g/l after growth on YES medium. P. verrucosum
shifts secondary metabolite biosynthesis after growth on YES medium from citrinin at low to
ochratoxin at elevated NaCl concentrations. The ochratoxin A biosynthesis of P. nordicum is accompanied
by an induction of the otapksPN gene, the gene of the ochratoxin A polyketide synthase. A mutant strain
unable to produce ochratoxin showed a drastic growth reduction under high NaCl conditions. Determination
of the dry weight and the chloride content in the mycelium of the P. nordicum wild type strain
and a non-ochratoxin A producing mutant strain showed a much higher increase of both parameters in
the mutant compared to the wild type. These results suggest, that the constant biosynthesis and
excretion of ochratoxin A, which itself contains a chloride atom, ensures a partial chloride homeostasis in
the fungal cell. This mechanism may support the adaptation of ochratoxin A producing Penicillia to NaCl
rich foods.

Aspergillus niger contains the cryptic phylogenetic species A. awamori

Aspergillus section Nigri is an important group of species for food and medical mycology, and biotechnology. The Aspergillus niger ‘aggregate’ represents its most complicated taxonomic subgroup containing eight morphologically indistinguishable taxa: A. niger, Aspergillus tubingensis, Aspergillus acidus, Aspergillus brasiliensis, Aspergillus costaricaensis, Aspergillus lacticoffeatus, Aspergillus piperis, and Aspergillus vadensis. Aspergillus awamori, first described by Nakazawa, has been compared taxonomically with other black aspergilli and recently it has been treated as a synonym of A. niger. Phylogenetic analyses of sequences generated from portions of three genes coding for the proteins b-tubulin (benA), calmodulin (CaM ),
and the translation elongation factor-1 alpha (TEF-1a) of a population of A. niger strains isolated from grapes in Europe revealed the presence of a cryptic phylogenetic species within this population, A. awamori. Morphological, physiological, ecological and chemical data overlap occurred between A. niger and the cryptic A. awamori, however the splitting of these two species was also supported by AFLP analysis of the full genome. Isolates in both phylospecies can produce the mycotoxins ochratoxin A and fumonisin B2, and they also share the production of pyranonigrin A, tensidol B, funalenone, malformins, and naphtho-g-pyrones. In addition, sequence analysis of four putative A. awamori strains
from Japan, used in the koji industrial fermentation, revealed that none of these strains belong to the A. awamori phylospecies.

The application of transcriptomics to understand the ecological reasons of ochratoxin a biosynthesis by Penicillium nordicum on sodium chloride rich dry cured foods

Penicillium nordicum and to some extent also P. verrucosumcan be found as contaminants on NaCl rich fermented foodslike ham, cheeses or vegetables. Both fungal species are ableto produce ochratoxin A. Ochratoxin A is a chloride containingmycotoxin which has toxic activities especially against the kidney.Further putative ochratoxin A producing species can befound in this environment. Recent results show that the productionof ochratoxin A increases the competitiveness of the producing fungi under salt stress conditions which occur in these types of foods. This increased competitiveness may explainthe frequent occurrence of these fungi in salt rich commodities.



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