Characterization and antimicrobial screening of secondary metabolite fractions from saprobic fungi

Fungal secondary metabolites are a rich source of bioactive compounds with significant pharmaceutical and agricultural potential, particularly for their antimicrobial properties. In this study, secondary metabolite fractions (F1, F2, and F3) were isolated from fourteen strains of saprobic fungi through a three-step solvent extraction using petroleum ether, ethanol, and water. The resulting fractions, soluble in their respective solvents, were analyzed by FTIR spectroscopy, with selected samples further characterized by NMR. Antimicrobial assays were conducted against seven pathogenic microorganisms. Among the tested fractions, the ethanol-soluble fractions (F2) generally exhibited the highest antimicrobial activity. Notably, F2 fractions from Trichoderma sp. DBM4197, Clonostachys rosea MFLU10-0261, and Stachybotrys parvispora MFLU10-0292 showed broad-spectrum inhibition against both Gram-positive and Gram-negative bacteria, as well as fungi. NMR analysis confirmed the presence of bioactive compounds, such as 6-substituted pyrenes and viridiofungins, in the F2 fraction of Trichoderma sp., which are known for their antimicrobial properties. These results indicate that the studied saprobic fungi are promising sources of secondary metabolites with potential for development into bactericidal agents.