Antibacterial and antilarval compounds from marine bacterium Pseudomonas rhizosphaerae

In order to obtain non-toxic, antifouling natural products from marine organisms, we studied on the marine bacterium Pseudomonas rhizosphaerae isolated from deep sea sediment. Bioassay-guided column chromatography techniques were used to separate and purify compounds. Extensive spectral analyses including 1D NMR spectra and GC-MS were employed for structure elucidation of the compounds. Antibacterial activity of the isolated compounds towards eight marine bacterial strains was measures by optical density, while antilarval activity was evaluated in settlement inhibition assays with laboratory-reared Balanus amphitrite and Bugula neritina larvae. In total, nine compounds including six diketopiperazine were obtained. Among them, cyclo-(Tyr-Pro), cyclo-(Tyr-Ile), cyclo-(Phe-Pro), cyclo-(Val-Pro), 3-phenyl-2-propenoic acid, and uracil had various antibacterial activities towards five marine fouling bacteria, furthermore, bis(2-ethylhexyl)phthalate, cyclo-(Tyr-Ile), cyclo-(Phe-Pro), cyclo-(Val-Pro), and 3-phenyl-2-propenoic acid showed antilarval effect on larval settlement of barnacle Balanus amphitrite and bryozoan Bugula neritina. The results suggested that marine bacterium Pseudomonas rhizosphaerae could produce potent antibacterial and antilarval diketopiperazine and benzene-type secondary metabolites.