Molecular and chemical monitoring of growth and ochratoxin a biosynthesis ofP. verrucosum in wheat stored at different moisture conditions.

The growth and ochratoxin A producing activity at the phenotypical and molecular level ofP. verrucosum in wheat stored at different relative moisture conditions have been followed. Growth has been measured by determination of colony forming units (cfu). The expression of the ochratoxin A polyketide synthase (otapksPV) has been followed over time by reverse transcriptase Real Time PCR, whereas the biosynthesis of ochratoxin A by the fungus has been followed by HPLC. The remoisted and inoculated wheat was kept in perforated plastic bags and stored in tower silos. The bags were adjusted to 24%, 19% and 14% (m/m) relative moisture and stored for 6 month (September 06 - February 06) at ambient temperatures. A high increase of the cfu number up to a level of about lx10(8) cfu/g could be observed in the 24% sample. Interestingly no growth could be detected in the 14% and 19% samples. This result was supported by the quantitative Real Time PCR data. In congruence with this growth behaviour ochratoxin A could be detected from the first to the last time point in the 24% sample. Interestingly the ochratoxin A amounts measured over time did not show increasing or constant values, but varied from higher to lower values. After storage of three month (November 2006) the ochratoxin A concentration in the wheat was highest. The expression of theotapksPV gene mirrors this behaviour. The expression of this gene also fluctuates around a certain value, showing high activity after three month of storage.