Abstract

Piscirickettsia salmonis is one of the major fish pathogens affecting Chilean aquaculture. This Gram-negative bacterium is highly infectious and is the etiological agent of Piscirickettsiosis. Little is currently known about how the virulence factors expressed by P. salmonis are delivered to host cells. However, it is known that several Gram-negative microorganisms constitutively release outer membrane vesicles (OMVs), which have been implicated in the delivery of virulence factors to host cells. In this study, OMVs production by P. salmonis was observed during infection in CHSE-214 cells and during normal growth in liquid media. The OMVs were spherical vesicles ranging in size between 25 to 145 nm. A proteomic analysis (LC-MS/ MS) for Multidimensional Protein identification technology (MudPit) of OMVs from P. salmonis identified 331 different proteins. Thus, several OMVs proteins have been identified to play a key role in P. salmonis pathogenesis, as well as some of these proteins form part of the type IV secretion system, flagella and pili structure. Several proteins involved in the process of bacterial conjugation were also identified. These results demonstrated that OMVs are an important contributor to the extracellular proteome and carry highly immunogenic proteins such as flagellins. Therefore, we propose that OMVs purified from P. salmonis could be evaluated as a vaccine prototype against Piscirickettsiosis.