New Pyrroline Isolated from Antarctic Krill-Derived Actinomycetes sp. LX-1 Combining with Molecular Networking.

Antarctic krill () of the family comprise one of the largest biomasses in the world and play a key role in the Antarctic marine ecosystem. However, the study of -derived microbes and their secondary metabolites has been limited. Chemical investigation of the secondary metabolites of the actinomycetes sp. LX-1 (in the family of ), isolated from , combined with molecular networking, led to the identification of 16 compounds - (purple nodes in the molecular network) and the isolation of one new pyrroline, nocarpyrroline A (), along with 11 known compounds -. The structure of the new compound was elucidated by extensive spectroscopic investigation. Compound exhibited broad-spectrum antibacterial activities against , , , and antifungal activity against in a conventional broth dilution assay. The positive control was ciprofloxacin with the MIC values of <0.024 µM, 0.39 µM, 0.39 µM, 0.39 µM, and 0.20 µM, respectively. Compound and compounds , , and displayed antifungal activities against and , respectively, in modified agar diffusion test. Prochloraz was used as positive control and showed the inhibition zone radius of 17 mm and 15 mm against and , respectively. All the annotated compounds - by molecular networking were first discovered from the genus . Nocarpyrroline A () features an unprecedented 4,5-dihydro-pyrrole-2-carbonitrile substructure, and it is the first pyrroline isolated from the genus . This study further demonstrated the guiding significance of molecular networking in the research of microbial secondary metabolites.