From extreme environments to fruit management: the antifungal potential of extremophilic yeasts to control Penicillium expansum on apple

Naganishia albida and Papiliotrema wisconsinensis strains isolated from extreme environments were tested as biocontrol agents (BCAs) against Penicillium expansum on apples and as inhibitors of patulin production through the biosynthesis of secondary metabolites. Each strain showed different capabilities in reducing P. expansum growth in in vitro and in vivo assays through different mechanisms of action. In particular, P. wisconsinensis strains showed the highest inhibition against the pathogen by producing VOCs. The strains displayed the highest amount of the main detected VOCs: 1-butanol, 3-methyl, propanoic acid, 2-methyl, butanoic acid, and phenylethyl alcohol. All the strains showed the same efficacy against P. expansum by producing non-VOCs in vitro. Conversely, in the in vivo assay, the cell strain suspensions completely inhibited rot symptoms and consequently the patulin production, probably due to the interaction between competition for nutrients and the activation of defence responses in the fruit. Conversely, yeast VOCs act at a metabolic level to modulate mycotoxin biosynthesis. In contrast, cell strain suspensions that include non-VOCs achieve broader protection through more direct antagonistic interactions. By FT-IR, the non-VOCs were mainly ascribed to a proteinaceous fraction and exopolysaccharides. This metabolic characterization emphasizes the importance of selecting BCAs based not only on their ability to inhibit fungal growth, but also on their impact on mycotoxin production.