Determination of ED₅₀ of transgenic cyanobacteria oral vaccine and safety evaluation on Danio rerio

Nowadays, in aquaculture, the popularity of antibiotics and the increase in the use of other drugs have made it easier for residual antibiotics and drugs to invade natural water bodies. The environmental effects of antibiotics in the ecosystem have caused more and more pollution to the water environment and threatened the survival of aquatic organisms. After strict regulation and control of the use of antibiotics, the use of genetically modified vaccines that can replace antibiotics has become more and more common. Cyanobacteria is a natural bait for shrimp seedlings. Directly feeding Litopenaeus vannamei with Synechococcus-expressedvp28 to control WSSV can play a role of “medicinal and food homology”. However, the problem facing the current application of transgenic cyanobacteria as a subunit vaccine is the safety of its environmental release. Danio rerio is one of the most commonly used model creatures. In the previous Synechococcus-expressedvp28 oral vaccine efficacy experiment, the feasibility of the oral vaccine was verified, showing that its efficacy and safety can be trusted. This environmental release experiment was built on this basis. In this study, Synechococcus-expressedvp28 were administered to L. vannamei to verify the effect of its dose gradient against WSSV and to determine its half effective dose (ED₅₀). After feeding D. rerio on the basis of this ED₅₀, the effects of the Synechococcus-expressed vp28 on aquatic organisms and water environment were explored by measuring the enzymatic indicators in D. rerio, observing the tissue sections, and the changes in nitrogen and phosphorus in the aquaculture water. The results of the study showed that with the increase of the dose of Synechococcus-expressedvp28 oral vaccine, the anti-WSSV efficacy of L. vannamei also increased and the measured ED₅₀ was 0.027 g. Feeding D. rerio by freeze-dried wild-type and transgenic Synechococcus with the shelled-out Artemia for 15 days, the body length and color of D. rerio were not significantly different. The CAT in the transgenic group was significantly lower than that blank and wild-type groups. There was no significant difference in SOD and POD between wild-type and transgenic groups. There was no significant difference in the liver and heart of D. rerio through the tissue section. The ammonia nitrogen in wild-type and transgenic groups was lower than that in the blank group, and there was no significant difference between total nitrogen and total phosphorus. The results of this study further showed that the Synechococcus-expressed vp28 can effectively enhance the anti-WSSV ability of L.vannamei, and as its dose increases, the disease resistance has a more significant expression. In the current experimental results, there is no obvious toxicological effect on D. rerio, and after feeding with Synechococcus-expressed vp28, it does not show a significant effect on the quality of aquaculture water. This shows that this subunit vaccine has less impact on aquatic organisms, and can provide a basis and more possibilities for subsequent industrial-scale applications and development.