Identification, characterization, antimicrobial activity and biocontrol potential of four endophytic fungi isolated from Amazonian plants

Endophytic fungi, which reside within plants without causing disease, are recognized for their ability to produce bioactive metabolites with antibacterial, antifungal, and antioxidant properties, as well as their role in enhancing plant defense mechanisms. Due to these valuable traits, endophytic fungi have attracted significant attention in biotechnology and microbiology. The four endophytic fungal strains were isolated from the leaves of four Amazonian plant species—Piper heterophyllum Ruiz & Pav. (Paichané negro), Peperomia sp., Faramea multiflora A. Rich. ex DC.(Yuracaré), and Dictyoloma vandellianum A. Juss. (Sombrerillo). Molecular identification via 18 S rDNA sequencing and NCBI-BLAST analysis, as well as morphological characterization, were carried out for the isolates. Ethyl acetate extracts were obtained from both the growth medium and the fungal biomass. Thin-layer chromatography (TLC) combined with various staining techniques was used to identify the main groups of chemical compounds present in the extracts. The extracts were then assessed for antibacterial activity through a minimum inhibitory concentration (MIC) assay. The antagonistic potential of four endophytic fungi was evaluated through confrontation with phytopathogenic fungi using the dual culture plate assay. The results from molecular and morphological identification revealed two Aspergillus strains (SMB-18 and SMB-22), one Fusarium strain (SMB-20), and one Alternaria strain (SMB-28). Chemical profiling revealed a diverse composition, including carotenoids, terpenes, flavonoids, and phenolic compounds. The MIC assay demonstrated strong antibacterial activity against Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, and Propionibacterium acnes), with MIC values ranging from 15.6 to 500 µg/mL. Additionally, antagonistic and biocontrol assays using dual-culture tests showed strong antifungal activity. Strains SMB-18, SMB-20, and SMB-22 effectively inhibited Helminthosporium sp. (58–80%), Fusarium oxysporum (37–50%), and Fusarium solani (51–57%), the well-known phytopathogenic fungi that affect potato crops. These findings highlight the potential of Amazonian endophytic fungi as sources of bioactive metabolites with promising applications in agriculture, medicine, and biotechnology, reinforcing the importance of biodiversity in bioprospecting.