Immunogenic proteins and their vaccine development potential evaluation in outer membrane proteins (OMPs) of Flavobacterium columnare

Flavobacterium columnare is a Gram-negative bacterium that causes columnaris disease in freshwater fish worldwide. Many studies have focused on the identification of protective antigens to aid in the development of novel vaccines against the disease. In this study, an immunoblotting approach was employed to identify immunogenic outer membrane proteins (OMPs) from F. columnare in two-dimensional electrophoresis (2-DE) map gels using antibacterial sera obtained from grass carp (Ctenopharyngodon idella), and anti-grass carp-recombinant Ig (rIg) monoclonal antibodies. Five unique immunogenic proteins, including the gliding motility lipoprotein GldJ (GldJ), hypothetical protein FCOL_13420 (Fco1), lipoprotein (Lip), F0F1 ATP synthase subunit beta (F0f1) and outer membrane efflux protein precursor (Omep), were characterized. Over-expression of these proteins in Escherichia coli DE3, and their immunogenicity and protective efficacy were evaluated in grass carp. The relative percent survival (RPS) of the groups immunized separately with recombinant GldJ, Lip and Omep was 72%, 64% and 68%, respectively when compared to control fish. Up-regulation of immuno-related genes and specific antibodies were detected in immunized fish and sera of immunized fish inhibited the growth of F. columnare. The results suggest that GldJ, Lip and Omep are major protective antigens and may be considered as novel candidates in the development of vaccines against columnaris disease in fish.