Utilization of recombinant Chlorella expressing dsRNA for protection against grouper nervous necrosis virus

In mammals and fish, dsRNA can induce the type I interferon (IFN-I), leading to the expression of antiviral and immune-related genes. The use of microalgae expressing dsRNA as an oral delivery system to activate innate immunity in fish has not been documented. In this study, wild Chlorella sorokiniana was transformed with NNV (nervous necrosis virus) RdRp and GIV (grouper iridovirus) ORF086R dsRNA expression vectors. The recombinant Chlorella strains effectively protected pearl gentian groupers ( Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) against NNV and reduced viral titers. The survival rates of the NNV RdRp and GIV ORF086R dsRNA treatment groups increased by 32 % and 38 %, respectively, compared with that of the control group. These findings indicate that recombinant Chlorella has the potential to be used as an oral delivery strategy for protection against NNV disease in groupers. • dsRNAs produced by reverse repeat sequences in microalgae can induce IFN. • This effect is similar to the dsRNAs generated by viral infection in fish. • Feeding grouper microalgae expressing dsRNA enhanced resistance to NNV infection. • The induction of IFN innate immunity by dsRNA does not exhibit sequence specificity.