Bioactive alkaloids and terpenoids from an endophytic fungus Aspergillus Keveii XVCY-9

Abstract

Endophytic fungi represent a special and promising microbial resource, known for their ability to promote the growth of host plants and metabolize attractive natural products. In this study, an endophytic fungus identified as Aspergillus keveii XVCY-9 was isolated from fresh tobacco leaves. Chemical purification of its ethyl acetate extracts led to the isolation of nine secondary metabolites. Their structures were elucidated through nuclear magnetic resonance (NMR) and mass spectrometry (MS) data as cinereain (1), carnequinazoline A (2), RES-1149-2 (3), carneamide B (4), carnequinazoline B (5), carneamide A (6), strobilactone A (7), bipolaricin R (8), and 6-epi-ophiobolin N (9). Among them, sesterterpenes 8 and 9 exhibited significant antibacterial effects against seven strains of plant and human pathogenic bacteria, with minimal inhibitory concentrations (MICs) ranging from 0.5 to 3.8 µg/mL, while compounds 1 and 2 showed moderate antimicrobial effects. Furthermore, compounds 2 and 7 could enhance the germination index of wheat seeds, which were even better than that of positive control indole-3-acetic acid. Additionally, compounds 2 and 3 can obviously promote the growth of wheat seedlings. These results suggest endophytic fungus A. keveii XVCY-9 is beneficial for the host plant due to the antibacterial and growth promoting effects of its secondary metabolites.