Antagonistic Activity and Mode of Action of Phenazine-1-Carboxylic Acid, Produced by Marine Bacterium Pseudomonas aeruginosa PA31x, Against Vibrio anguillarum In vitro and in a Zebrafish In vivo Model

Phenazine and its derivatives are very important secondary metabolites produced from spp. and have exhibited broad-spectrum antifungal and antibacterial activities. However, till date, there are few reports about marine derived and its production of phenazine metabolites. In this study, we isolated a marine strain PA31x which produced natural product inhibiting the growth of C312, one of the most serious bacterial pathogens in marine aquaculture. Combining high-resolution electro-spray-ionization mass spectroscopy and nuclear magnetic resonance spectroscopy analyses, the functional compound against was demonstrated to be phenazine-1-carboxylic acid (PCA), an important phenazine derivative. Molecular studies indicated that the production of PCA by PA31x was determined by gene clusters and in its genome. Electron microscopic results showed that treatment of with PCA developed complete lysis of bacterial cells with fragmented cytoplasm being released to the surrounding environment. Additional evidence indicated that reactive oxygen species generation preceded PCA-induced microbe and cancer cell death. Notably, treatment with PCA gave highly significant protective activities against the development of C312 on zebrafish. Additionally, the marine derived PCA was further found to effectively inhibit the growth of agricultural pathogens, NP1 and JM1. Taken together, this study reveals that marine derived PCA carries antagonistic activities against both aquacultural and agricultural pathogens, which broadens the application fields of PCA.