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

## TL;DR

This study examines how temperature, pH, and humidity affect the growth of a fungus found on pears and its production of a harmful toxin called penitrem A.

## Contribution

The study identifies optimal environmental conditions for growth and toxin production in Penicillium crustosum OM1, and links gene expression to these conditions.

## Key findings

- P. crustosum OM1 grows best at 25 °C, pH 4.5, and 98% humidity.
- Penitrem A production peaks at 22 °C, pH 6.5, and 98% humidity.
- Four penitrem A biosynthetic genes are upregulated in a toxin-conducive medium.

## Abstract

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.