Pseudopeptides of Marine Vibrio spp. from Taiwan and Their Combined Treatment Effects with Commercial Antibiotics.

Vibrio strains, identified by 16S rDNA, were isolated from the marine environment surrounding Taiwan, revealing diverse bioactive effects, such as iron-chelating and antimicrobial activities. Notably, the hierarchical clustering dendrogram of mass spectrum profiles of the Vibrio strains using matrix-assisted laser desorption ionization time-of-flight, in contrast to the phylogenetic tree based on 16S rDNA sequencing analysis, exhibited a strong correlation with their observed bioactivities. Within this set, global natural products social molecular network analysis by LC-HRMS/MS highlighted that three strains, Vibrio tubiashii DJW05 - 1, Vibrio japonicus DJW05 - 8, and Vibrio fortis DJW21 - 4, shared similar bioactive pseudopeptides in the same cluster. Subsequent chromatographical isolation and purification yielded an unprecedented unsaturated diketopiperazine, (Z)-3-(2-methylpropylidene)-2,3-dihydropyrrolo[1,2-a]pyrazine-1,4-dione (1: ), along with a series of diketopiperazines, and a potential new annotated pseudopeptide (2: ), as well as three pseudopeptides, including andrimid (10: ), moiramide B (11: ), and moiramide C (12: ), and several alkaloids from V. tubiashii DJW05 - 1. Further investigation into the combined applications of the major antimicrobial compound and commercial antibiotics revealed that andrimid (10: ) displayed significant inhibitory effects against gram-positive Staphylococcus aureus, and gram-negative Escherichia coli, Salmonella typhimurium, and Acinetobacter baumannii, but not Pseudomonas aeruginosa. Nevertheless, the potential for synergistic and additive effects of andrimid (10: ) with certain antibiotics remains, presenting valuable prospects for medicinal applications.