Production of Ochratoxin A and Citrinin and the Expression of Their Biosynthetic Genes from Penicillium verrucosum in Liquid Culture.

ABSTRACT

Penicillium verrucosum is a fungal pathogen capable of producing two mycotoxins of concern, ochratoxin A (OTA) and citrinin (CIT). The production profile of these two mycotoxins is not well understood but could help mitigate co-contamination in the food supply. As such, the production of OTA and CIT from P. verrucosum DAOMC 242724 was investigated under different growing conditions in liquid culture. We found that among the different liquid media chosen, liquid YES (yeast extract sucrose) medium induced the highest production of both OTA and CIT, when P. verrucosum DAOMC 242724 was cultured in stationary mode. Shake culture significantly reduced the amounts of OTA and CIT produced. Among all culture conditions tested, far greater amounts of CIT were produced compared to OTA. Consequently, upon transcriptomic data analysis, a statistically significant increase in the expression of CIT biosynthetic genes was easier to detect than the expression of OTA biosynthetic genes. Our study also revealed that the putative biosynthetic gene clusters of OTA and CIT in P. verrusocum DAOMC 242724 are likely distinct from each other. It appears that despite sharing a highly similar structure, the isocoumarin rings of OTA and CIT are each assembled by a specialized polyketide synthase enzyme. Our data identified a putative nonreducing polyketide synthase responsible for assembling the carbo-skeleton of CIT. In contrast, a highly reducing polyketide synthase appears to be involved in the biosynthesis of OTA.