Characterization Of Edwardsiella Piscicida MviN And Development Of Bacterial Vector Vaccine Against Turbot Reddish Body Iridovirus

Edwardsiella piscicida is an important bacterial pathogen that affects the health of marine aquaculture fish worldwide.Because it is an intracellular pathogen,traditional inactivated vaccines are not effective in preventing ascites disease.Therefore,the design of a kind of new vaccine based on the pathogenic mechanism is the basis and premise for the development of Edwardsiella vaccine against edwardsienosis.The two-component system has been confirmed to be closely related to the virulence of Edwardsiella piscicida.But it mainly focused on the downstream regulation pathways of the two-component system EsrA-EsrB in the early stage of the laboratory,and the upstream regulation network of EsrA-EsrB was less studied.In the previous study,39 kinds of potential esrB regulatory factors were screened out by transposon insertion sequencing(TIS)technology.Among them,it was speculated that MviN played an active role in the transcription of esrB.In the work,it was verified that MviN functions in activating esrB transcription.Also,MviN exerted different function to regulate the expression of esrB in the early and late growth stages.Finally,the effect of MviN was investigated on the regulation of E.piscicida colonization in the host,and MviN was showed to influence E.piscicida colonization by regulating EsrB.In summary,it was found that MviN is an important regulator of esrB,and is conducive to the colonization of E.piscicida in turbot,which helps to improve the upstream regulatory pathway of esrB.Turbot reddish body iridovirus is one of the main viral pathogens in turbot farming in our country,and there is currently no effective treatment.At present,the main capsid protein MCP is the immunoprotective antigen of choice for the development of fish virus vaccines.But MCP-based vaccine design mainly focused on DNA vaccines and subunit vaccines,and both of which had limitations of weak immunogenicity.In the early stage of the laboratory,the multi-site deletion strain WED of E.piscicida was developed,which had a significant protective effect against edwardsienosis in turbot.In addition,the laboratory has developed a kind of dual-control system,IronQS,with the response to both bacterial density based on the luxl/luxR system from Vibrio fischeri and iron ion density.The expression of IronQS is tightly regulated on WED.Based on the above research,in the work a kind of vector vaccine candidate was developed using WED as a bacterial vector and IronQS-mcp as a dual-inducible expression regulatory plasmid to express major capsid protein MCP of turbot reddish body iridovirus.It was showed that the carrier vaccine WED/IronQS-mcp could cause a continuous increase in total protein levels and specific antibody levels of serum,and efficiently activate expression of superoxide dismutase and transcription of Mx and other immune factors.MCP could be expressed in turbot for a long time.To sum up,the carrier vaccine WED/IronQS-mcp could activate the humoral and cellular immunity of turbot and provide long-term protective antigens.It is great potential for commercial development of vaccines,which provides new ideas for the development of viral vaccines and multivalent vaccines.In short,this study conducted a preliminary exploration and the development of vector vaccines of the major pathogens of turbot,which provided new strategies for the rational design of turbot vaccine.