Screening metabolites for potential biological activities of fungal strains isolated from a grassland ecosystem

Fungal metabolites possess a broad range of functions, ranging from antibiotics to mycotoxins. These metabolites can be retained either in the cell, secreted into the surrounding environment, or exuded by guttation. This study screened metabolites produced by selected soil fungi isolated from grassland soils for potential industrial applications. Three different soil fungal strains were isolated: two Penicillium spp. (PEN1 and PEN2) and one Aspergillus sp. (ASP1). Of them, PEN2 and ASP1 isolates showed guttation. Chemical screening was carried out using Thin Layer Chromatography (TLC), selected qualitative chemical tests, and Fourier Transform Infrared spectroscopy (FT-IR). Fungal extracts in ethyl acetate and fungal guttation droplets were tested for antibacterial (against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922), antifungal, and toxin production abilities with positive and negative controls. All fungal isolates showed different levels of metabolite production, with the highest being ASP1 and PEN2, which showed guttation as well. FT-IR spectral bands of ethyl acetate extracts of ASP1, PEN1, and PEN2 revealed the presence of C-H (alkyl), C-H (aldehyde), C≡N (nitrile), C-H (aromatic), C=O (aldehyde), N-H (amine), and C-N (amine) as functional groups in extracted compounds. The highest antibacterial effect against S. aureus was observed from broth extracts of PEN2 (with an inhibition zone diameter of 14.78±0.11 mm) and ASP1 against E. coli (17.67±0.18 mm). The highest antifungal activity against Cladosporium sp. was displayed by PEN2 (13.70±0.02 mm), with no effect by PEN1. The seed assay showed zero germination of seeds for ethyl acetate broth extracts of all three tested fungal strains, indicating a phytotoxic effect of their metabolites. The study concludes that fungi isolated from grassland soils have shown the ability to produce bioactive metabolites that can be used in various industrial applications, including pharmaceutical and agricultural.