Identificação de metabólitos secundários com potencial antimicrobiano produzidos pelo fungo endofítico Lasiodiplodia sp. isolado do Ipê rosa (Handroanthus impetiginosus)

Abstract

The antimicrobial resistance of pathogens has become a problem of huge dimensions that affects the quality of life of the worldwide population. The discovery of natural products that could overcome this situation is a very promising feature. Endophytes have been widely studied, as they can produce many bioactive substances with therapeutic potentials, such as antimicrobial activity. The present work aims to identify secondary metabolites that contribute to the antimicrobial activity of the fermentation products obtained from the endophytic fungus Lasiodilodia sp., isolated from Handroanthus impetiginosus leaves. To achieve this goal, five crude extracts with different polarity was

obtained from the fermentation broth (Ld-Hex, Ld-Chlo, Ld-EA, and Ld-EA+) and from the mycelium (Ld-EAm), which were fractionated. Crude extracts, fractions, and sub-fractions were tested for their antimicrobial activity against pathogens. Listeria monocytogenes and Candida parapsilosis were the most sensitive pathogens, the crude extracts Ld-Chlo and Ld-AEm exhibited the highest inhibition values: MIC of 12.5-25 µg.mL -1 . The fractions were tested against Listeria monocytogenes and Candida albicans and those who showed higher activity were sub-fractionated. Antimicrobial activity improved after fractionation, probably due to a pre-concentration of bioactive compounds; however, the subfractions activities varied, showing the importance of organic compounds mixtures to develop a better antimicrobial activity. The fractions derived from Ld-Chlo extract were evaluated by GC-MS identifying four known compounds with recognized antimicrobial activity: (Z) -docos-13-enamide, (Z) - octadec-9-methyl enoate, (Z) -octadec-9-enamide, and dodecanamide, which is probably related to these fractions antimicrobial activity. In another fraction, LdAEm-9, indole-3-carboxylic acid was purified by HPLC, elucidating its chemical structure by NMR. There are several biological activities described for this metabolite, and it may be responsible for the antimicrobial activity of this fraction. On the other hand, the analysis of AEm68-C and AEm68-E sub- fractions by NMR spectroscopy and HRESIMS allowed identifying four known aromatic compounds: 4-hydroxybenzoic acid, indole-3-carboxylic acid, 4- hydroxymellein, and 4-hydroxyphenylacetamide. The identification of organic compounds in mixtures through the analysis of 1D and 2D NMR spectra is a relevant outcome of the present work. The conclusions stand out that Lasiodiplodia sp. endophyte is capable of producing compounds with antimicrobial activity, observed throughout the fractionation carried out and through the isolation and NMR/HRESIMS-based identification of known bioactive aromatic compounds.