Recombinant baculovirus mediates dsRNA specific to rr2 delivery and its protective efficacy against WSSV infection

Shrimp injection with dsRNA targeting the microsporidian EHP polar tube protein reduces internal and external parasite amplification

The microsporidian Enterocytozoon hepatopenaei (EHP) is a major threat to shrimp health worldwide. Severe EHP infections in shrimp cause growth retardation and increase susceptibility to opportunistic infections. EHP produces spores with a chitin wall that enables them to survive prolonged environmental exposure. Previous studies showed that polar tube extrusion is a prerequisite for EHP infection, such that inhibiting extrusion should prevent infection. Using a proteomic approach, polar tube protein 2 of EHP (EhPTP2) was found abundantly in protein extracts obtained from extruded spores. Using an immunofluorescent antibody against EhPTP2 for immunohistochemistry, extruded spores were found in the shrimp hepatopancreas (HP) and intestine, but not in the stomach. We hypothesized that presence of EhPTP2 might be required for successful EHP spore extrusion. To test this hypothesis, we injected EhPTP2-specific double-stranded RNA (dsRNA) and found that it significantly diminished EHP copy numbers in infected shrimp. This indicated reduced amplification of EHP-infected cells in the HP by spores released from previously infected cells. In addition, injection of the dsRNA into EHP-infected shrimp prior to their use in cohabitation with naïve shrimp significantly (p < 0.05) reduced the rate of EHP transmission to naïve shrimp. The results revealed that EhPTP2 plays a crucial role in the life cycle of EHP and that dsRNA targeting EHP mRNA can effectively reach the parasite developing in host cells. This approach is a model for future investigations to identify critical genes for EHP survival and spread as potential targets for preventative and therapeutic measures in shrimp.

Effects of length and sequence of long double-stranded RNAs targeting ribonucleotide reductase 2 of white spot syndrome virus (WSSV) on protective efficacy against WSSV

Long double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) has been a well-known mechanism against white spot syndrome virus (WSSV) in cultured shrimp. In the present study, we investigated the protective efficacy of dsRNAs targeting the ribonucleotide reductase 2 (rr2) gene of WSSV according to length and target sequence location. To produce different lengths of dsRNAs, the 640 bp rr2 fragment (fragment I) was split into two equal 320 bp fragments (fragment II and III), then each 320 bp fragment was redivided into two 160 bp fragments (fragment IV, V, VI, and VII). After the synthesis of seven kinds of dsRNA fragments, dsRNAs with the same length were mixed with each other, then used for the evaluation of dsRNA's length effect in Penaeus vannamei. The result showed that 160 bp long dsRNAs were as effective as 320 and 640 bp long dsRNAs in the protection of shrimp against WSSV infection, suggesting that the dsRNA length of 160 bp would be enough to be used as RNAi-mediated WSSV suppression in P. vannamei. However, as the 160 bp long dsRNAs used in the length effect experiment were not a single dsRNA population but a mixture of 160 bp dsRNA fragments covering the parent 640 bp long dsRNA, the sequence effect was not included in this RNAi efficacy. In the experiments to know the effect of not only length but also sequence of rr2-targeting long dsRNAs on the protective efficacy against WSSV, dsRNAs with a length of 640 bp (fragment I) and 320 bp (fragment II, III) showed a constant high defense ability, but the protection degree of long dsRNAs with a length of 160 bp was different depending on the kinds of the fragment, suggesting that the RNAi efficacy of some rr2-targeting long dsRNAs with a length of 160 bp might have sequences that are variable according to experimental conditions. In conclusion, this study showed that the protective ability of long dsRNAs in shrimp against WSSV infection can be affected by the length and sequence of the long dsRNAs.

Potential dsRNAs can be delivered to aquatic for defense pathogens

The use of antibiotics to facilitate resistance to pathogens in aquatic animals is a traditional method of pathogen control that is harmful to the environment and human health. RNAi is an emerging technology in which homologous small RNA molecules target specific genes for degradation, and it has already shown success in laboratory experiments. However, further research is needed before it can be applied in aquafarms. Many laboratories inject the dsRNA into aquatic animals for RNAi, which is obviously impractical and very time consuming in aquafarms. Therefore, to enable the use of RNAi on a large scale, the methods used to prepare dsRNA need to be continuously in order to be fast and efficient. At the same time, it is necessary to consider the issue of biological safety. This review summarizes the key harmful genes associated with aquatic pathogens (viruses, bacteria, and parasites) and provides potential targets for the preparation of dsRNA; it also lists some current examples where RNAi technology is used to control aquatic species, as well as how to deliver dsRNA to the target hydrobiont.

Oral administration of Saccharomyces cerevisiae displaying VP28-VP24 confers protection against white spot syndrome virus in shrimp

White spot syndrome virus (WSSV) is the major pathogen that leads to severe mortalities in cultured shrimp worldwide. The envelope proteins VP28 and VP24 of WSSV are considered potential vaccine candidate antigens. In this study, we utilized a Saccharomyces cerevisiae (S. cerevisiae) surface display system to demonstrate the feasibility of this platform for developing a vaccine candidate against WSSV. EBY100/pYD1-VP28-VP24 was generated, and the fusion protein VP28-VP24 was present on the surface of S. cerevisiae. Penaeus vannamei (P. vannamei) was used as an animal model. Oral administration of EBY100/pYD1-VP28-VP24 could induce significant activities of immune-related enzymes such as superoxide dismutase (SOD) and phenoloxidase (PO). Importantly, WSSV challenge indicated that oral administration of EBY100/pYD1-VP28-VP24 could confer 100% protection with a corresponding decrease in the viral load. The collective results strongly highlight the potential of a S. cerevisiae-based oral vaccine as an efficient control strategy for combating WSSV infection in shrimp aquaculture.

Co-expression of double-stranded RNA and viral capsid protein in the novel engineered Escherichia coli DualX-B15(DE3) strain

Background

Viruses cause significant economic losses to shrimp aquaculture worldwide. In severe cases, they can lead to 100% mortality within a matter of days, hence the aquaculture industry requires antiviral strategies to minimize economic impacts. Currently, a double-stranded RNA (dsRNA)-based platform has been proven effective at a laboratory scale. The bottleneck for its industrialization is the lack of low-cost, efficient and practical delivery approaches. In an effort to bridge the gap between laboratory and farm applications, virus-like particles (VLP) have been used as nanocarriers of dsRNA. However, the implementation of this approach still suffers from high costs and a lengthy procedure, co-expression of subunits of VLP or capsid proteins (CPs) and dsRNA can be the solution for the problem. CP and dsRNA are traditionally expressed in two different E. coli hosts: protease-deficient and RNase III-deficient strains. To condense the manufacturing of dsRNA-containing VLP, this study constructed a novel E. coli strain that is able to co-express viral capsid proteins and dsRNA in the same E. coli cell.

Results

A novel bacterial strain DualX-B15(DE3) was engineered to be both protease- and RNase III-deficiency via P1 phage transduction. The results revealed that it could simultaneously express recombinant proteins and dsRNA.

Conclusion

Co-expression of viral capsid proteins and dsRNA in the same cell has been shown to be feasible. Not only could this platform serve as a basis for future cost-effective and streamlined production of shrimp antiviral therapeutics, it may be applicable for other applications that requires co-expression of recombinant proteins and dsRNA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02148-8.

Meta-analysis of antiviral protection of white spot syndrome virus vaccine to the shrimp

Currently, white spot syndrome virus (WSSV) is one of the most serious pathogens that impacts shrimp farming around the world. A WSSV vaccine provides a significant protective benefit to the host shrimp. Although various types of vaccines against WSSV have emerged, the immune effects among them were not compared, and it remains unclear which type of vaccine has the strongest protective effect. Meanwhile, due to the lack of effective routes of administration and immunization programs, WSSV vaccines have been greatly limited in the actual shrimp farming. To answer these questions, this study conducted a comprehensive meta-analysis over dozens of studies and compared all types WSSV vaccines, which include sub-unit protein vaccines, whole virus inactivated vaccines, DNA vaccines and RNA-based vaccines. The results showed that the RNA-based vaccine had the highest protection rate over the other three types of vaccines. Among the various sub-unit protein vaccines, VP26 vaccine had the best protective effects than other sub-unit protein vaccines. Moreover, this study demonstrated that vaccines expressed in eukaryotic hosts had higher protection rates than that of prokaryotic systems. Among the three immunization modes (oral administration, immersion and injection) used in monovalent protein vaccines, oral administration had the highest protection rate. In natural conditions, shrimp are mostly infected by the virus orally. These results provide a guide for exploration of a novel WSSV vaccine and help facilitate the application of WSSV vaccines in shrimp farming.

An efficient method for multigene co-interference by recombinant Bombyx mori nucleopolyhedrovirus

Bombyx mori Nucleopolyhedrovirus (BmNPV), which is a member of the Baculoviridae family, is a significant pathogen of the silkworm. The infection of BmNPV is often lethal and causes about 20% loss of cocoon in the silk industry annually. To explore the effects of different gene inhibition strategies on the replication cycle of baculovirus, we constructed the mutant virus to infect BmN cells directly and further identified ie0, ie1, and gp64 as the essential viral genes of BmNPV. To elucidate the significance of the inhibition effect of different interference strategies, we characterized and constructed the recombinant BmNPV that carried a single or multigene-interfering cassette. The results showed that the inhibition effect of dsie1 on target gene expression, virus titer, and silkworm mortality was significantly better than that of dsie0 and dsgp64. It also showed that the dsie1 interference produced fewer progeny virions and was less lethal, which indicates that ie1 played a more critical role in the BmNPV replication cycle. Furthermore, the inhibitory effect of the virus titer and mortality indicated that the multigene co-interference constructed by the baculovirus expression system was significantly better than the interference of any single-gene (p < 0.05). In summary, the strategy of multigene synergy can achieve the function of continuous interference and provide a new platform for the breeding of silkworm disease resistant. In addition, this strategy improves the various traits of the silkworm.