Identification and evaluation of an outer membrane protein OmpU from a pathogenic Vibrio harveyi isolate as vaccine candidate in turbot (Scophthalmus maximus)

Aims: The main aims of this study were to clone and express a new outer membrane protein U (OmpU) from a pathogenic Vibrio harveyi SF-1 and investigate its immune efficiency as a vaccine candidate against V. harveyi infection in turbot (Scophthalmus maximus). Methods and Results: In this study, a new gene, ompU was cloned from the genomic DNA of pathogenic V. harveyi SF-1. The ompU gene encoded a 35 kDa protein, which was purified by Ni-NTA His-Bind Resin column. A DNA vaccine was constructed by inserting ompU gene into pEGFP-N1 plasmid. Turbot were injected intramuscularly with the purified OmpU protein and the recombinant pEGFP-N1/ompU plasmid, respectively. The fish vaccinated with the purified OmpU protein were completely protected with a relative per cent of survival (RPS) of 100% against pathogenic V. harveyi infection. Efficient protection was also found in the pEGFP-N1/ompU vaccinated group, with a RPS of 51.4%. Significant specific antibody responses were detected in the vaccinated turbot by indirect enzyme-linked immunosorbent assay. Conclusions: A new OmpU was cloned and expressed. Both OmpU protein vaccine and DNA vaccine showed good immune protections in turbot. Significance and Impact of the Study: The OmpU was identified to be a new effective vaccine candidate and could be used as subunit vaccine and DNA vaccine for disease control caused by pathogenic V. harveyi.