A Marine Mesorhizobium sp. Produces Structurally Novel Long-Chain N -Acyl- l -Homoserine Lactones

Our study focused on aMesorhizobium sp. that is phylogenetically affiliated by 16S rRNA gene sequence to other marine and saline bacteria of this genus. Liquid chromatography-mass spectrometry investigations of the extract obtained from solid-phase extraction of cultures of this bacterium indicated the presence of severalN -acyl homoserine lactones (AHLs), with chain lengths of C10 to C16 . Chromatographic separation of the active bacterial extract yielded extraordinarily large amounts of two unprecedented acylated homoserine lactones, 5-cis -3-oxo-C12 -homoserine lactone (5-cis -3-oxo-C12 -HSL) (compound 1) and 5-cis -C12 -HSL (compound 2). Quorum-sensing activity of compounds 1 and 2 was shown in two different biosensor systems [Escherichia coli MT102(pSB403) andPseudomonas putida F117(pKR-C12)]. Furthermore, it was shown that both compounds can restore protease and pyoverdin production of an AHL-deficientPseudomonas aeruginosa PAO1lasI rhlI double mutant, suggesting that these signal molecules maybe used for intergenus signaling. In conclusion, these data indicate that the quorum-sensing activity of compounds 1 and 2 is modulated by the chain length and functional groups of the acyl moiety. Additionally, compound 1 showed antibacterial and cytotoxic activities.