Abstract
Vibrio vulnificus, a bacterial species that inhabits brackish waters, is an opportunistic pathogen of humans. V. vulnificus infections can cause acute gastroenteritis, invasive septicemia, tissue necrosis, and potentially death. Virulence factors associated with V. vulnificus include the capsular polysaccharide (CPS), lipopolysaccharide, flagellum, pili, and outer membrane vesicles (OMVs). The aims of this study were to characterize the morphology of V. vulnificus cells and the formation and arrangement of OMVs using cryo-electron microscopy (cryo-EM). cryo-EM and cryo-electron tomography imaging of V. vulnificus strains grown in liquid cultures revealed the presence of OMVs (diameters of ∼45 nm for wild-type, ∼30 nm for the unencapsulated mutant, and ∼50 nm for the non-motile mutant) in log-phase growth. Production of OMVs in the stationary growth phase was limited and irregular. The spacing of the OMVs around the wild-type cells was in regular, concentric rings. In wild-type cells and a non-motile mutant, the spacing between the cell envelope and the first ring of OMVs was ∼200 nm; this spacing was maintained between subsequent OMV layers. The size, arrangement, and spacing of OMVs in an unencapsulated mutant was irregular and indicated that the polysaccharide chains of the capsule regulate aspects of OMV production and order. Together, our results revealed the distinctive organization of V. vulnificus OMVs that is affected by expression of the CPS.
Highlights
Vibrio vulnificus, a halotrophic Gram-negative bacterium that lives in brackish estuarine waters, is associated with shellfish in natural environments (DePaola et al, 1997) and is an opportunistic pathogen of humans (Jones and Oliver, 2009)
Vibrio vulnificus cells were dispersed on the cryo-electron microscopy (cryo-EM) grids as 1.5–3 μm long bacteria
Arrangement of outer membrane vesicles (OMVs) Is Unique to V. vulnificus
Summary
A halotrophic Gram-negative bacterium that lives in brackish estuarine waters, is associated with shellfish in natural environments (DePaola et al, 1997) and is an opportunistic pathogen of humans (Jones and Oliver, 2009). Little is known about the ultrastructure of V. vulnificus or the structure of CPS, flagellum, pili, and OMVs or their relationships to other cellular components
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