Activity of Secondary Metabolites from Marine-Derived Trichoderma longibrachiatum ST-27 Against Vibrio harveyi.

Aquaculture and environmental challenges continue to constrain the industry's sustainable development. The misuse of antimicrobial agents has accelerated the dissemination of resistance genes, posing a serious threat to both animal husbandry and human health. Thus, the discovery of novel antibiotic alternatives is of great significance for sustainable aquaculture and public health protection. Marine fungi have recently attracted considerable attention in natural product research due to their ability to produce structurally diverse and bioactive secondary metabolites under unique marine conditions. In this study, the marine-derived strain Trichoderma longibrachiatum ST-27 was subjected to large-scale fermentation. The crude extract (ST-27-3) was fractionated into seven components using gel permeation chromatography, followed by further purification with silica gel column chromatography and semi-preparative high-performance liquid chromatography (HPLC). Two compounds were isolated, among which two were identified as pentadecaibin IV (1) and trichorzianine 1938 (2) by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) analyses. Their antibacterial activities were subsequently evaluated. Pentadecaibin IV and trichorzianine 1938 are linear small-molecule polypeptides. Antibacterial assays showed that trichorzianine 1938 exhibited concentration-dependent inhibitory activity against Vibrio harveyi VH306, with the highest inhibition observed at 300 µg/mL. These findings demonstrate that T. longibrachiatum ST-27 is a rich source of peptaibol-type metabolites with antibacterial, antifungal, insecticidal, and cytotoxic properties. The results highlight the potential of marine-derived peptaibols as promising lead compounds for the development of novel antimicrobial agents and provide a theoretical basis for their application in aquaculture disease control.