Outer membrane vesicles (OMVs) are nano-sized proteoliposomes shed from the cell envelope of all Gram-negative species. OMVs are now recognized as a generalized secretion pathway that provides a means to transfer cargo to other bacterial cells and eukaryotic cells. OMVs play an important role in pathogenesis, delivering virulence factors to the host cells, including toxins, adhesins, and immunomodulatory molecules. Moritella viscosa strain Gram-negative pathogen causes winter ulcer disease in several marine fish species. However, the levels of mortality in lumpfish have not been fully understood.
First, the aim of this study, we determined the lethal dose (LD50 ) of M. viscosa could infect and produce the pathogenesis of winter ulcer and mortality in lumpfish used to evaluate the efficacy of the vaccine. Lumpfish was injected with M. viscosa intraperitoneal (i.p.) with 3.1 x 107 colony-forming units (CFU) fish-1 had rapid mortality with more 50% of fish mortality and typical clinical signs of ulcer disease after 5 days post-infection.
Secondly, to characterize an OMVs isolated from M. viscosa grown in medium iron-rich and iron-limited conditions. OMVs were characterized by transmission electron microscopy and protein analysis. M. viscosa OMVs in both conditions are spheres of 39.8–370 nm diameter that contains small RNA and DNA. The main OMVs proteins have a molecular size of 45, 30 and 20 kDa . OMVs isolated from iron-limited condition harbor an additional protein of approximately 60 kDa which is absent in OMVs isolate from bacteria grown under iron-rich conditions. The protein profile of the 60 kDa protein band had an enzyme of Metal-dependent carboxypeptidase, Glucose-6-phosphate isomerase, Glucose-6-phosphate isomerase and transport systems including the peptide ABC transporter, extracellular solute-binding protein, and Oligopeptide transport system, permease protein B.
In summary, our results provide strong that M. viscosa could induce the ulcer disease in lumpfish. These OMVs products may partially explain the play key roles in pathogenesis of M. viscosa . Further studies will be conducted to characterize OMVs cargo, toxicity, and utility as vaccine candidates.