Unravelling the Role of Non-Clustered Polyketide Synthases and Key Metabolites in Ochratoxin a Accumulation by Penicillium nordicum in Salt-Rich Environments

Ochratoxin A (OTA) accumulation by Penicillium nordicum is enhanced at high salt concentrations. The genes involved in OTA biosynthesis include a polyketide synthase (PKS), although other PKSs outside the cluster could influence OTA production. This study aimed to evaluate a potential new PKS involved in OTA biosynthesis and the metabolites related to this mycotoxin. Optimised protocols were designed for the gene expression analysis of five genes that encoded the previously reported PKS to be overexpressed in dry-cured meat products (n2, n3, n4, n5 and n6). Their expression was tested in two P. nordicum strains (Pn15 and Pn856) grown in CYA medium with different salt concentrations. Fungal mycelia were used for gene expression analyses and metabolomics. Three genes (n3, n4 and n6) seem to be related to OTA biosynthesis in Pn856. However, n2 might be involved in OTA degradation. The lack of correlations between the genes studied and OTA in Pn15 could be due to the low OTA levels quantified. The metabolites coniferyl alcohol and 6-hydroxy-8-methoxy-3-methylisochroman were positively correlated to OTA, and 3-methylbutanoic acid and cephalosporolide E might be used as indicators to predict OTA. These results show the complex regulation and influence of PKS proteins on OTA levels.