Molecular monitoring of environmental conditions influencing the induction of ochratoxin A biosynthesis genes in Penicillium nordicum

A real-time polymerase chain reaction (PCR) system specific for the ochratoxin A polyketide synthase gene (otapksPN) of Penicillium nordicum has been used to analyze environmental conditions, influencing the induction of that key gene of the ochratoxin A biosynthetic pathway. Generally, the induction of that gene coincides very well with the biosynthesis of ochratoxin A, demonstrating that its induction can be used as a molecular signal to monitor ochratoxin A production. It could be shown, that the expression of the otapksPN gene is greatly dependent on the media used. In YES medium expression is highest, followed by minimal medium which support ochratoxin A production and minimal medium which suppresses ochratoxin A production. The amount of ochratoxin A produced shows the same tendency. The amount produced is highest on YES medium and decreases successively to the two minimal media. The system was also used to determine the influence of environmental parameters like temperature, pH and NaCl concentration on the expression of the otapksPN gene and on ochratoxin A production in parallel. It could be shown that under acidic conditions, below pH 5.0, the expression of the otapksPN gene as well as the ochratoxin A concentration were reduced. In case of salt concentration again both measures coincide, having both highest values at increasing NaCl concentrations. In case of the temperature, however, expression of the otapksPN gene was uncoupled to ochratoxin A production. The expression was high at all temperatures tested, however, clear differences in the biosynthesis of ochratoxin A by P nordicum could be observed at the different temperatures, showing highest production at 25degreesC. The importance of these data are discussed with reference to the natural habitat of P nordicum.