Antibacterial and antibiofilm activities of the metabolites isolated from the culture of the mangrove-derived endophytic fungus Eurotium chevalieri KUFA 0006

Abstract

Five previously undescribed metabolites, including acetylquestinol, two prenylated indole 3-carbaldehyde derivatives, an anthranilic acid derivative and an isochromone derivative, were isolated, in addition to eleven known compounds: palmitic acid, ergosterol 5,8-endoperoxide, emodin, physcion, questin, questinol, (11S, 14R)-cyclo(tryptophylvalyl), preechinulin, neoechinulin E, echinulin and eurocristatine, from the culture of the endophytic fungus Eurotium chevalieri KUFA 0006. The structures of the previously undescribed compounds were established based on an extensive 1D and 2D NMR spectral analysis as well as HRMS and IR data. In case of 2-(2, 2-dimethylcyclopropyl)-1H-indole-3-carbaldehyde and 6, 8-dihydroxy-3-(2S-hydroxypropyl)-7-methylisochromone, the absolute configurations of their stereogenic carbons were established based on comparison of their experimental and calculated ECD spectra. All the compounds, except for palmitic acid and ergosterol 5, 8-endoperoxide, were evaluated for their antibacterial and antibiofilm activities against two Gram-positive and two Gram-negative bacteria, as well as multidrug-resistant isolates from the environment. Emodin not only exhibited moderate antibacterial activity against the Gram-positive bacteria but also showed strong synergistic association with oxacillin against MRSA Staphylococcus aureus.

Keywords: Anthraquinones; Antibacterial activity; Antibiofilm; Diketopiperazines; Eurotium chevalieri; Isochromone; Mangrove-derived fungus; Prenylated indoles; Trichocomaceae.