Penicillium oxalicum has been used as a biocontrol fungus in agriculture for many years, but the antimicrobial substances are still uncertain. Herein, we isolated a linear peptide named Sanxiapeptin in the culture broth of Penicillium oxalicum SG-4 collecting from the Three Gorges riparian zone. Sanxiapeptin exhibited potent inhibitory effect on citrus green mold Penicillium digitatum, the main fungi responsible for postharvest decay. Sanxiapeptin was elucidated as composing of five amino acids, which were β-amino-α-methoxybutyric acid (Amoba), N-Me-l-Thr, d-Thr, N-Me-l-Val and l-Ser. By analyzing three chemically synthesized oligopeptides with similar structures, we found that the first amino acid of Amoba was crucial to the antifungal activity, as was the methylation of peptide bond. Sanxiapeptin may act as an antimicrobial agent by affecting the function of cell membranes or walls. The antimicrobial spectrum, safety and stability analysis supported that Sanxiapeptin was a promising antifungal agent for citrus preservation.
Keywords: Antifungal pentapeptide; Citrus preservation; Penicillium digitatum; Peptide bond methylation; Postharvest decay; β-Amino-α-methoxybutyric acid.
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