Abstract

Background: Endophytic fungi are considered a source of novel activities, compounds and biotechnological processes with great and underexplored potential. The aims of this paper were: a) to evaluate the antibiotic activity of mangrove endophytic fungi against the human pathogens Staphylococcus aureus, Salmonela typhi and Escherichia coli and against the phytopathogen Xantomonas axonopodis citri; b) to elucidate the structure of the antibiotic produced by the endophytic fungus Hypocrea virens strain 89(3), using spectroscopic methods, mainly 1D and 2D NMR, as well as mass spectra and comparison with previously published data.

Methods: The selection of the endophytic fungi producer of antibiotics was based on agar piece method. The pure substance (viridiol) was obtained by carrying out biological tests with the extract and its fractions against pathogenic bacteria (Escherichia coli), and this study was monitored by NMR spectroscopy. Viridiol was isolated from the mangrove endophytic fungus H. virens, which was obtained from branches of Avicennia nitida. The structure of the compound was elucidated by spectroscopic methods, mainly 1D and 2D NMR spectroscopy and confirmed by mass spectrometry.

Results: In bioassays, compound viridiol showed antimicrobial activity against Escherichia coli, with an MIC of 64 µg/ml. The antibiotic-producing strain was identified as H. virens using internal transcribed spacer (ITS) sequence data. The spectroscopic methods employed were an efficient means of elucidating the structure of antibiotic viridiol.

Conclusion: The isolation of a bioactive substance using 1H NMR monitoring was highly successful because it showed step by step the spectral signals concerning the bioactive substance from crude extract to pure substance. This is the first report of antimicrobial activity by viridiol against E. coli, a medically important pathogen.

Keywords: Endophytic fungi, Hypocrea virens, NMR spectroscopy, Trichodema, viridiol, biological assay.

Graphical Abstract