A new aquatic pathogen inhibitor produced by the marine fungus Aspergillus sp. LS116

In this study, a fungal strain LS116 with antibacterial activity against aquatic pathogen Vibrio harveyi was screened out from sponge-associated fungi by Oxford cup method. According to its morphological characteristics and internal transcribed spacer (ITS) analysis, the active strain belonged to the genus Aspergillus. A bioactivity-guided approach was conducted to identify the antibacterial substances in the culture extract of strain LS116, a new C23 steroid with bicyclo [4.4.1]A/B ring, named aspergillsteroid A (1), and a known C25 steroid with the same structure skeleton, neocyclocitrinol B (2), were isolated and purified by column chromatography and HPLC (high-performance liquid chromatography) for the first time. Their chemical structures were determined by HRESIMS (high-resolution electrospray ionization mass spectroscopy) spectrometry, NMR (nuclear magnetic resonance) spectroscopy, and CD (circular dichroism). Among them, compound 1 displayed significant antibacterial activity against V. harveyi with a MIC value of 16 mu g/mL. The study demonstrated that compound 1 can be considered as a new promising agent for the control of aquatic disease in the future.