Outer membrane vesicles are vehicles for the delivery of V ibrio tasmaniensis virulence factors to oyster immune cells

Abstract

Summary Vibrio tasmaniensis LGP 32, a facultative intracellular pathogen of oyster haemocytes, was shown here to release outer membrane vesicles ( OMV s) both in the extracellular milieu and inside haemocytes. Intracellular release of OMV s occurred inside phagosomes of intact haemocytes having phagocytosed few vibrios as well as in damaged haemocytes containing large vacuoles heavily loaded with LGP 32. The OMV proteome of LGP 32 was shown to be rich in hydrolases (25%) including potential virulence factors such as proteases, lipases, phospholipases, haemolysins and nucleases. One major caseinase/gelatinase named V sp for vesicular serine protease was found to be specifically secreted through OMV s in which it is enclosed. V sp was shown to participate in the virulence phenotype of LGP 32 in oyster experimental infections. Finally, OMV s were highly protective against antimicrobial peptides, increasing the minimal inhibitory concentration of polymyxin B by 16‐fold. Protection was conferred by OMV titration of polymyxin B but did not depend on the activity of V sp or another OMV ‐associated protease. Altogether, our results show that OMV s contribute to the pathogenesis of LGP 32, being able to deliver virulence factors to host immune cells and conferring protection against antimicrobial peptides.

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