Rotation of Vibrio fischeri Flagella Produces Outer Membrane Vesicles That Induce Host Development.

Using the squid-vibrio association， we aimed to characterize the mechanism through which Vibrio fischeri cells signal morphogenesis of the symbiotic light-emitting organ. The symbiont releases two cell envelope molecules， peptidoglycan (PG) and lipopolysaccharide (LPS) that， within 12 h of light organ colonization， act in synergy to trigger normal tissue development. Recent work has shown that outer membrane vesicles (OMVs) produced by V. fischeri are sufficient to induce PG-dependent morphogenesis; however， the mechanism(s) of OMV release by these bacteria has not been described. Like several genera of both beneficial and pathogenic bacteria， V. fischeri cells elaborate polar flagella that are enclosed by an extension of the outer membrane， whose function remains unclear. Here， we present evidence that along with the well-recognized phenomenon of blebbing from the cell's surface， rotation of this sheathed flagellum also results in the release of OMVs. In addition， we demonstrate that most of the development-inducing LPS is associated with these OMVs and that the presence of the outer membrane protein OmpU but not the LPS O antigen on these OMVs is important in triggering normal host development. These results also present insights into a possible new mechanism of LPS release by pathogens with sheathed flagella.