Study on antifungal secondary metabolites of Fusarium oxysporum HU0174, an endophytic fungus in Pu tree
Infection by pathogenic fungi is one of the main causes of post harvest fruit and vegetable rot. It not only causes significant economic losses, but some fungi also produce fungal toxins, posing a potential threat to human life safety. The use of antifungal agents can greatly inhibit the occurrence and development of post harvest fruit and vegetable diseases. However, increasing research and practice have shown that the large-scale long-term use of fungicides can lead to increased pathogen resistance. At the same time, as people’s awareness of health and environmental protection continues to increase, the development of safer, lower toxicity, and lower residue new natural antifungal agents is receiving increasing attention.

Fusarium fungi are a widely distributed group of fungi that can produce fungal toxins such as fumonisin and T-2 toxin, as well as metabolites with diverse structures and potential medicinal value such as alkaloids, peptides, amides, terpenes, quinones, and pyranose ketones. In the screening of antibacterial activity of endophytic bacteria in plants in the early stage, it was found that a rice fermentation product of endophytic Fusarium sp. HU0174 had good antagonistic activity against citrus green mold. To this end, natural product chemistry methods were used to isolate, identify, and evaluate the antifungal activity of secondary metabolites in the rice fermentation product of this fungus.

Cyclic peptide microbial derived antifungal agents have the characteristics of easy degradation and low residue, among which natamycin has been widely used as a natural antibacterial agent in the food industry in multiple countries and regions. Cyclic ester peptide compounds have biological activities such as antibacterial and anti-tumor effects, and are increasingly attracting widespread attention. The research on the antibacterial activity of cyclic ester peptide compounds is relatively mature, and some have been used in clinical practice, including antibiotics colistin and daptomycin, which can be used to treat diseases caused by multidrug-resistant Gram negative and Gram positive bacteria, respectively. There is relatively little research on the antifungal activity, including the inhibitory effects of clavivopsins A and B on Candida albicans, Aspergillus fumigatus, and Aspergillus niger, with MIC values of 8, 4, and 16 μ g/mL, respectively; Verlamens A and B showed strong inhibitory effects on mango anthracnose pathogen, with MIC values of 4.9 and 9.8 μ g/mL, respectively. Studies have shown that acutatum B and C exhibit strong antagonistic activity against apple black fungus, apple chain disk fungus, and rice spiral cavity fungus, with the same MIC values of 1.1 and 10 μ g/mL, respectively. At the same time, the homolog fusaripeptide A of acutatum B shows strong inhibitory effects on Candida albicans, Candida albicans, Candida albicans, and Aspergillus fumigatus, with IC50 values ranging from 0.11 to 0.24 μ M, slightly lower than amphotericin B.
This study isolated and identified seven compounds, including five cyclic ester peptides and two heterocyclic compounds, from the ethyl acetate fraction of rice fermentation products of Fusarium sp. HU0174, an endophytic fungus in Pinus massoniana. Among them, compound 1 was a new compound, enriching the diversity of secondary metabolites produced by Fusarium. The antifungal activity results showed that the cyclic ester peptide compounds acutatum A-D (1-4) had inhibitory effects on citrus green mold and crescent mold at 200 μ g, but had no inhibitory activity on Aspergillus niger and Aspergillus flavus. This indicates that the fungal antagonistic activity of the compound acutatum cyclic ester peptide has strong specificity, which preliminarily clarifies the antifungal active substance basis of Fusarium sp. HU0174 and has certain reference value for the development of antifungal agents from new microbial sources.