Many bacteria use extracellular signaling molecules to coordinate group behavior, a process referred to as quorum sensing (QS). However, some QS molecules are hydrophobic in character and are probably unable to diffuse across the bacterial cell envelope. How these molecules are disseminated between bacterial cells within a population is not yet fully understood. Here we show that the marine pathogenVibrio harveyipackages the hydrophobic QS molecule CAI-1, a long-chain amino ketone, into outer membrane vesicles. Electron micrographs indicate that outer membrane vesicles of variable size are predominantly produced and released into the surroundings during stationary phase ofV. harveyi, which correlates with the timing of CAI-1-dependent signaling. The large vesicles (diameter < 55 nm) can trigger a QS phenotype in CAI-1 non-producingV. harveyiandV. choleraecells. Packaging of CAI-1 into outer membrane vesicles might stabilize the molecule in aqueous environments and facilitate its distribution over distances.IMPORTANCEFormation of membrane vesicles is ubiquitous among bacteria. These vesicles are involved in protein and DNA transfer and offer new approaches for vaccination. Gram-negative bacteria use among others hydrophobic signaling molecules for cell-cell communication, however due to their hydrophobic character it is unclear how these molecules are disseminated between bacterial cells. Here we show that the marineVibrio harveyipackages one of its quorum sensing molecules, the long-chain ketone CAI-1, into outer membrane vesicles (OMVs). Isolated CAI-1-containing vesicles trigger a quorum sensing phenotype in CAI-1 non-producingV. harveyiand also inV. choleraecells. Packaging of CAI-1 into OMVs not only solubilize, stabilize and concentrate this class of molecules, but facilitate their distribution between bacteria that live in aqueous environments
