Optimization Of Culture Conditions And Evaluation Of Immunoprotection Effect On Crucian Carp Of HisJ Gene Deficient Strain Of Aeromonas Veronii TH0426

Aeromonas veronii is a human-animal-aquatic commensal pathogen,which is widely distribute in natural environment.In recent years,the number of diseases caused by A.veronii has increased each year,which is a major threat to aquaculture and the public health safety.The his J gene could effect the flagellation of A.veronii TH0426.The his J gene influences the shedding,virulence,biofilm formation,adhesion and invasion of pathogen,which is closely related to virulence,and plays a critical role in the pathogenicity of A.veronii TH0426.Gene deficiency vaccines are low virulence live microorganism that without additional adjuvants.The low virulence vaccines are less costly and have a long-lasting effect on the body,resulting in a stronger immune response.To prevent fish diseases in aquaculture,the abuse of antibiotics threatens the water environment and public health.As the idea of green health gains traction,the development of vaccines to combat fish diseases has been accelerated.In this study,the most suitable type and amount of medium and optimal culture conditions were determined by optimizing the medium and culture conditions for the his J gene deficient strain of A.veronii TH0426.After immunization and subsequent tests were conducted using crucian carp（Carassius auratus）,the following results were obtained.1.The optimum medium was 13.92 g/L tryptone,2.4 g/L soluble starch and 9.42 g/L dipotassium hydrogen phosphate.2.Optimal culture conditions are 5%inoculum,p H 7.6,temperature 38°C,speed 220 r·min^-1 and salinity 1%.3.The expression of flagellum-related virulence genes fli C,fli E,flg B,flg C,flg E and mot A were all up-regulated in the flagellum-deficient strains cultured after optimisation compared to before optimisation,and the loadings of heart,liver,spleen and kidney tissues were also decreased compared to before optimisation.The immunoprotection rate was 66.67%before optimisation and 77.78%after optimisation,and the immunoprotection rate increased after optimisation compared to before optimisation.Ig M,SOD,ALP and C3 immune-related indexes were increased compared with those before optimization.In summary,the optimal medium and optimum culture conditions for the his J gene deficient A.veronii TH0426 strain were determined by single-factor test and response surface analysis,resulting in an increase in the concentration and amount of viable bacteria.The findings indicated that the virulence of A.veronii TH0426 his J gene-deficient strain was reduced and the immune protection rate was increased,which provided a theoretical foundation for the extensive production of A.veronii attenuated vaccine.