Construction of Fish Vaccine via Heterologously Biosynthesizing Bacterial Type III Secretion System

Abstract

Abstract The delivery of antigens into the host cells through type III secretion system (T3SS) is an effective strategy employed by bacteria to induce host immune responses and facilitate colonization. To achieve optimal immersion protection with a vaccine, we employed a T3SS antigens delivery system, which is heterologously biosynthesized in an avirulent Aeromonas salmonicida DBFF01, to deliver heterologous antigen as a vaccine carrier. A recombinant GAPDH (rGAPDH) protein, which was fused with a Photorhabdus luminescens TT01 translocation signal and chaperone SlcT, was constructed as an antigen. Then, we investigated the extracellular secretion of heterologous expression rGAPDH, as well as its expression during the infection of Hela cells. Western blotting demonstrated that heterologously biosynthesized T3SS could exhibited functional activity. More importantly, T3SS-expressing A. salmonicida strains had no toxicity or side effects when tested with hematoxylin and eosin assays. The immune protection of DBFF01-T3SS-Δphage-rGAPDH and DBFF01-T3SS-rGAPDH against the pathogen E. tarda in grass carp was evaluated at 59.1% and 37.4% by the relative percent survival (RPS), respectively. In addition, we analyzed the expression profiles of multiple immune-related genes after challenge. Notably, complement component 3 (C3) was up-regulated in the livers of grass carp injected with T3SS-expressing A. salmonicida strains, indicated that C3 may play an assisting role in repairing liver tissue damaged by E. tarda. In conclusion, our study found that T3SS is an effective antigen delivery system, which employed the type III secretion system to deliver recombinant immunogenic protein rGAPDH in grass carp against E. tarda, and we suggested that the vaccine could induce corresponding immune responses and facilitate colonization in fish.