Abstract
Outer membrane porins, as the major components of Gram-negative bacterial membrane proteins, have been proven to be involved in interactions with the host immune system and potent protective antigen candidates against bacterial infection in fish. Outer membrane porin F (OmpF) is one of the major porins of Yersinia ruckeri (Y. ruckeri), the causative agent of enteric red mouth disease of salmonid and non-salmonid fish. In the present study, the molecular characterization and phylogenetic analysis of OmpF gene was studied, heterogenous expression, immunogenicity and protective immunity of OmpF were systemically evaluated as a subunit vaccine for channel catfish against Y. ruckeri infection. The results showed that OmpF gene was highly conserved among 15 known Yersinia species based on the analysis of conserved motifs, sequences alignment and phylogenetic tree, and was subjected to negative/purifying selection with global dN/dS ratios value of 0.649 throughout the evolution. Besides, OmpF was also identified to have immunogenicity by western blotting and was verified to be located on the surface of Y. ruckeri using cell surface staining and indirect immunofluorescence assays. Moreover, recombinant OmpF (rtOmpF) as a subunit vaccine was injected with commercial adjuvant ISA763, significantly enhanced the immune response by increasing serum antibody levels, lysozyme activity, complement C3 activity, total protein content, SOD activity, immune-related genes expression in the head kidney and spleen, and survival percent of channel catfish against Y. ruckeri infection. Thus, our present results not only enriched the information of molecular characterization and phylogenetics of OmpF, but also demonstrated that OmpF holds promise to be used as a potential antigen against Y. ruckeri infection in fish.
Highlights
Yersinia ruckeri (Y. ruckeri) is a Gram-negative rod-shaped enterobacterium and the causative agent of enteric red mouth disease (ERM), one of the most serious septicemic bacterial disease of salmonid fish species [1]
The two-dimensional topology structures of Y. ruckeri Outer membrane porin F (OmpF) showed that OmpF located extracellular without any transmembrane regions and the signal peptide sequences located into the Motif 1 domain (Figure 2B)
As the major components and one of the most abundant proteins in the outer membrane, bacterial porin proteins play a critical role in bacterial pathogenesis and interactions with the host immune system [68, 69]
Summary
Yersinia ruckeri (Y. ruckeri) is a Gram-negative rod-shaped enterobacterium and the causative agent of enteric red mouth disease (ERM), one of the most serious septicemic bacterial disease of salmonid fish species [1]. It has been reported that Y. ruckeri has been increasingly widespread and been detected as an important pathogen of salmonid fish in many other countries [2,3,4,5,6] since its isolation in North American [7,8,9,10]. Apart from salmonids, Y. ruckeri can infect other non-salmonid fish species including common carp [11], whitefish [12], sturgeon [13,14,15], and channel catfish [16, 17]. Genetically engineered vaccines based on conserved and potent protective antigen genes, are increasingly urgent and need to be developed
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