Estudo químico e biológico de fungos endofíticos isolados de Deguelia duckeana

Abstract

In recent years, the chemical study of endophytic fungi has shown that they produce a variety of new secondary metabolites. Additionally, fungal endophytes can develop the ability to produce substances similar to their host plants, becoming an ecological alternative in the search for bioactive compounds. Therefore, the objective of this study was to assess the chemical and biological potential of endophytic fungi isolated from Deguelia duckeana in terms of bioactive substance production. Healthy leaves of D. duckeana were collected and disinfested. After incubating leaf fragments on solid PDA medium, endophytic fungi were isolated and purified. For obtaining methanolic mycelium crude extracts, the endophytic fungi (14 strains) were cultivated on a reduced scale in Czapek medium supplemented with 0.2% yeast extract at 30 °C, under shaking conditions for 20 days. Methanolic extracts were subjected to thin-layer chromatography (TLC), 1H nuclear magnetic resonance (1H-NMR), and antibacterial evaluation to select a fungus for large-scale cultivation. The selected fungus was cultivated under the same initial conditions, and its mycelia were extracted with dichloromethane and methanol. The methanolic extract was partitioned with ethyl acetate, yielding the hydro-methanolic and ethyl acetate phases. Extracts and phases underwent chromatographic methods, NMR, gas chromatography-mass spectrometry (GC-MS), antibacterial assay and toxicity assessment against Artemia salina. 28 endophytic fungi were isolated from D. duckeana leaves, of which 14 fungi were selected for submerged cultivation. Thin-layer chromatography analyses of fungal methanolic extracts revealed possible aromatic substances, alkaloids, and terpenes. 1H-NMR analyses confirmed the presence of such chemical classes. Chemical screening directed the selection to the fungi encoded as BDDD14-G3, BDDD23-G5, and BDDD25-G4, identified as Diaporthe sp., Colletotrichum sp., and Diaporthe oculi, respectively. The methanolic extract of D. oculi stood out in the antibacterial assay and was the selected fungus for large-scale cultivation. The dichloromethane extract of D. oculi underwent chromatographic fractionation, leading to the isolation of ergosterol and a mixture of triglycerides. GC-MS analysis of the triglycerides identified the presence of 13 fatty acids, with palmitic acid (27.9%) and stearic acid (16.5%) being the predominant methylated fatty acids in the mixture. The dichloromethane extract and the hydro-methanolic and ethyl acetate phases of the methanolic extract showed no toxicity against Artemia salina. The dichloromethane extract inhibited 49.75% of Escherichia coli growth. These results contribute to the chemical and biological characterization of the endophytic microbiota of the species D. duckeana. Additionally, this is the first report of a chemical study on D. oculi. Future studies may continue to explore the biotechnological potential of other fungi from D. duckeana, as well as identify other substances present in the extracts of Diaporthe oculi with potential biological activities.