Exploring the potential of Flavobacterium covae catalase and DNA starvation/stationary phase protein as recombinant protein vaccines against columnaris disease in channel catfish.

Columnaris disease, caused by Flavobacterium covae, is a principal cause of mortality in the catfish industry that can lead to several million dollars in annual production losses. This Gram-negative bacterium is an opportunistic pathogen that manifests as a biofilm on the host's mucosal surfaces as the disease progresses. Recent work in our lab identified the upregulation of specific F. covae biofilm genes after stimulation with channel catfish mucus. We have previously demonstrated the effectiveness of using a F. covae recombinant protein for bath immersion vaccination of catfish to protect against columnaris disease. The current study evaluated additional F. covae recombinant proteins for their efficacy as vaccine formulations delivered by bath immersion. F. covae catalase and DNA starvation/stationary phase proteins were cloned and expressed in E. coli and purified under native conditions. Different groups of fish were immunized with the recombinant protein(s) mixed with an immersion adjuvant or sham immunized with adjuvant alone. Nine weeks post-immunization, all groups were challenged with F. covae and the vaccinated groups showed significant increases in survival (13-45 %) when compared to the adjuvant only control group. No antigen specific skin mucosal IgM antibodies were detected via ELISA; however, RT-qPCR analyses of innate and adaptive immune genes suggested induction of an immune response occurred among vaccinated groups. Additional delivery strategies to enhance the catfish immune response to F. covae recombinant protein vaccines is underway to optimize their use in the production environment.