Construction of an attenuated glutamyl endopeptidase deletion strain of Nocardia seriolae

The glutamyl endopeptidase homolog of Nocardia seriolae (GluNS) has been proved to be a potential virulence factor in our previous study. Present investigation was carried out to construct an attenuated N. seriolae strain by deletion with GluNS gene and evaluate its protective immunity in head snakehead. A deletion strain (NS-AGluNS) was established by knockout of gene GluNS from wild strain N. seriolae ZJ0503 via homologous recombination. The LD50 of NS-AGluNS in 3.41 x 106 cfu/mL was significantly increased than that of wild strain in 4.75 x 105 cfu/mL, indicating that the virulence of N. seriolae has been attenuated with the knockout of GluNS. Meanwhile, applying NS-AGluNS as an attenuated live vaccine to immune hybrid snakehead, the non-specific immunity parameters (serum LYZ, POD, ACP, and AKP activities), specific antibody (IgM) titers production and immune -related genes (MHCI alpha, CD4, and IL-8) expression were up-regulated in different tissues, which indicated that they were able to trigger humoral and cell-mediated immune responses. Furthermore, the protective efficacy in hybrid snakehead after vaccination with NS-AGluNS shown 73.53% relative percentage survival (RPS). Taken together, the attenuated NS-AGluNS was obtained successfully and it could elicit strong immune response and supply protective efficacy to hybrid snakehead against N. seriolae wild strain.

Automated summary

The study demonstrated that the glutamyl endopeptidase homolog of Nocardia seriolae (GluNS) is a potential virulence factor. An attenuated N. seriolae strain, NS-AGluNS, was successfully constructed by deleting the GluNS gene, which can induce immune responses and provide protection to hybrid snakehead.