Effects of Temperature, pH, and Relative Humidity on Growth of Penicillium crustosum OM1 Isolated from Pears and Its Penitrem A Production.

Penitrem A, an indole-diterpenoid neurotoxin, is produced by several species of Penicillium on cereal grains, meat, dairy products, and fruits. Penicillium crustosum is a well-known penitrem A producer, but much is unknown about physiological characteristics of P. crustosum. In this study, we isolated penitrem A-producing P. crustosum OM1 from pears, and investigated the influence of temperature, pH, and relative humidity [RH] on its growth and penitrem A production. The fungal species exhibited the highest growth at 25 °C and pH 4.5 on mYES4 under RH 98%, whereas it produced the highest level of penitrem A at 22 °C and pH 6.5 on the same media under RH 98%. Furthermore, RT-qPCR analysis of six penitrem A biosynthetic genes (ptmB, ptmJ, ptmK, ptmO, ptmS, and ptmT) expression in P. crustosum OM1 showed that the four penitrem A biosynthetic genes (ptmJ, ptmK, ptmO, and ptmS) were up-regulated in mYES4 (penitrem A conducive medium), whereas they were not in mMEB (penitrem A non-conducive medium). Our results demonstrated that the three key environmental factors significantly affected the growth of P. crustosum OM1 and its penitrem A production. These findings could help find efficient methods to prevent penitrem A contamination from fresh fruits including pears.