The role and fate of patulin in apple-associated fungal-fungal interactions

Fungal secondary metabolites (SMs) have attracted significant attention due to their pharmaceutical applications and negative impact as food contaminants. However, less attention has been paid to understanding the ecological role of SMs for the producer and their natural microbial community. To investigate this, we performed co-cultures of SM deficient mutant strains and wild type fungi isolated from mouldy windfall apples. The competitiveness of Penicillium expansum mutant strains was tested in co-cultures with Monilinia fructigena on apple puree agar. Remarkably, the absence of patulin production in P. expansum lead to a loss of antagonism against M. fructigena, revealing a nuanced ecological role that extends beyond the involvement of patulin in host pathogenicity. Furthermore, chemical analysis revealed biotransformation of patulin by M. fructigena, pointing to a more complex interplay mediated by SMs for fungal species inhabiting the same ecosystem.