title: Gene expression as an indication for ochratoxin A biosynthesis inPenicillium nordicum.
abstract: The expression level of theotapksPN gene ofPenicillium nordicum was determined by Reverse Transcription Real Time PCR in relation to several growth parameters known to have an influence on ochratoxin A biosynthesis, like pH, medium composition and temperature. Generally there was a good correlation between the expression level of this key gene and ochratoxin A biosynthesis. The results, which were obtained by Real Time PCR for a single gene, could generally be confirmed by microarray analysis with a whole set of genes related to ochratoxin A biosynthesis. Growth conditions which favour the expression of the ochratoxin A biosynthetic genes also resulted in the biosynthesis of ochratoxin A by the fungal culture, indicating that the influence of abiotic parameters is mediated via the regulation of transcription of the ochratoxin A biosynthetic genes. The influence of several parameters, like pH, salt concentration and temperature on the expression of the ochratoxin A biosynthetic genes has been analysed. Optimum conditions for the activation of the ochratoxin A biosynthesis genes were: pH 6.0-8.0, 25 °C and a sodium chloride concentration of 20 g/l. This was paralleled by the capacity ofP. nordicum to produce ochratoxin A under the same conditions. After combining the most inhibitory conditions (15 °C, sodium chloride 10 g/l, pH 5.0) nearly a complete deactivation of the ochratoxin A biosynthetic genes could be observed resulting in a complete abolishment of ochratoxin A biosynthesis. In contrast, a high expression and a high production of ochratoxin A could be observed after growth ofP. nordicum under more optimal conditions (25 °C, 20 g/1 sodium chloride, pH 8.0).
authors.affiliation: Federal Research Centre for Nutrition and Food, Location Karlsruhe, Haid-und-Neu-Str. 9, 76131, Karlsruhe, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schmidt-Heydt
authors.forename: R
authors.initials: R
authors.lastname: Geisen