Characterization of Outer Membrane Vesicle Release in Vibrio vulnificus

The production of outer membrane vesicles (OMVs) by Gram-negative bacteria is an active process that takes place when a section of the outer membrane bulges off to form periplasm-containing vesicles without causing bacterial lysis. OMVs directly influence bacteria-host interaction and pathogenesis through their ability to modulate immune responses, contribute to biofilm formation, and deliver toxins and other virulence factors to host cells [1]. The ability of OMVs to bind to eukaryotic membranes makes them potential delivery vehicles for antibiotics and candidate vaccines against pathogens such as Vibrio cholerae , indicating their significant biotechnological potential [2]. OMVs have also been recognized to be important components of bacterial biofilms. V. vulnificus is a Gram-negative bacterium which colonizes filter-feeding shellfish. This opportunistic pathogen is responsible for 95% of seafood-related deaths in the United States and is categorized as a category B biodefense priority pathogen by the National Institutes of Allergies and Infectious Diseases [3]. Virulence in V. vulnificus is regulated by structural components such as cellular appendages (flagella and pili) and the capsular polysaccharide. Even though their contribution to bacterial pathogenesis is widely recognized, the mechanism of OMV production is not yet understood. Here, we use multiple TEM imaging techniques to characterize the unusual secretion and spatial arrangement of OMVs. We present further cryo-electron tomography data [4] (Fig. 1) of OMV release and distribution in Vibrio vulnificus and several of its mutant forms in order to link these results to known differences in virulence. Because of the low contrast of cryo TEM,