Isolation, identification, and proteomic analysis of outer membrane vesicles of Riemerella anatipestifer SX-1.

Riemerella anatipestifer, belonging to Weeksellaceae family Riemerella, is a bacterium that can infect ducks, geese, and turkeys, causing diseases known as duck infectious serositis, new duck disease, and duck septicemia. We collected diseased materials from ducks on a duck farm in China and then isolated and purified a strain of serotype 1 R. anatipestifer named SX-1. Animal experiments showed that SX-1 is a highly virulent strain with an LD value of 10 CFU/mL. The complete genome sequence was obtained. The complete genome sequence of R. anatipestifer SX-1 was 2,112,539 bp; 847 genes were involved in catalytic activity, and 445 genes were related to the cell membrane. The total length of the repetitive sequences was 8746 bp. Four CRISPR loci were predicted in R. anatipestifer strain SX-1, and 4 genomic islands were predicted. Concentration and ultra-high-speed centrifugation were used to extract the outer membrane vesicles of R. anatipestifer SX-1. The OMVs were extracted successfully. Particle size analysis revealed the size and abundance of particles: 147.4 nm, 94.9%; 293.6 nm, 1.1%; 327.2 nm, 1.1%; 397.2 nm, 0.3%; and 371.8 nm, 1.1%. The average size was 173.5 nm. Label-free proteomic technology was used to identify proteins in the outer membrane vesicles. ATCC 11845 served as the reference genome sequence, and 148 proteins were identified using proteomic analysis, which were classified into 5 categories based on their sources. Among them, 24 originated from cytoplasmic proteins, 4 from extracellular secreted proteins, 27 from outer membrane proteins, 10 from periplasmic proteins, and 83 from unknown sources. This study conducted a proteomic analysis of OMVs to provide a theoretical basis for the development of R. anatipestifer OMVs vaccines and adjuvants and lays the foundation for further research on the relationship between the pathogenicity of R. anatipestifer and OMVs.