Oral vaccination with envelope protein VP28 against white spot syndrome virus in Procambarus clarkii using Bacillus subtilis as delivery vehicles

Oral vaccination of fish against vibriosis using spore-display technology

Oral vaccines are highly demanded by the aquaculture sector, to allow mass delivery of antigens without using the expensive and labor-intensive injectable vaccines. These later require individual handling of fish, provoking stress-related mortalities.

One possible strategy to create injection-free vaccine delivery vehicles is the use of bacterial spores, extremely resistant structures with wide biotechnological applications, including as probiotics, display systems, or adjuvants. Bacterial spores, in particular those of Bacillus subtilis, have been shown to behave as mucosal vaccine adjuvants in mice models. However, such technology has not been extensively explored against fish bacterial disease.

In this study, we used a laboratory strain of B. subtilis, for which a variety of genetic manipulation tools are available, to display at its spores surface either a Vibrio antigenic protein, OmpK, or the green fluorescence protein, GFP. When previously vaccinated by immersion with the OmpK- carrying spores, zebrafish survival upon a bacterial challenge with V. anguillarum and V. parahaemolyticus, increased up to 50 - 90% depending on the pathogen targeted. Further, we were able to detect anti-GFP-antibodies in the serum of European seabass juveniles fed diets containing the GFP-carrying spores and anti-V. anguillarum antibodies in the serum of European seabass juveniles fed the OmpK-carrying spores containing diet. More important, seabass survival was increased from 60 to 86% when previously orally vaccinated with in-feed OmpK- carrying spores. Our results indicate that B. subtilis spores can effectively be used as antigen-carriers for oral vaccine delivery in fish.

Modulation of growth performance, antioxidant capacity, non-specific immunity and disease resistance in largemouth bass (Micropterus salmoides) upon compound probiotic cultures inclusion

An 8-week feeding trial was conducted to evaluate the effects of dietary supplementation of compound probiotic cultures (CPC; Bacillus subtilis, Lactobacillus plantarum and Saccharomyces cerevisiae) on the growth performance, antioxidant capacity, non-specific immunity and disease resistance of juvenile largemouth bass. Triplicate groups of largemouth bass (average weight 42.05 ± 0.02 g), with a destiny of 30 individuals per tank, were fed diets supplemented with different concentration of compound probiotic cultures (CPC) (0%, CPC (0.0); 0.5%, CPC (0.5); 1.0%, CPC (1.0); 2.0%, CPC (2.0)). After the feeding trial, tissue samples of largemouth bass were collected and the challenge test with Aeromonas hydrophila was performed. Results indicated that the CPC supplementation produced no significant difference on the growth performance, feed utilization and body composition of largemouth bass, while significantly increased the cumulative survival rate in the Aeromonas hydrophila challenge test. Meanwhile, the inclusion of CPC elevated the hepatic antioxidant capacity, and the highest activity of antioxidant enzymes, including T-AOC, CAT, GPx and T-SOD, was observed in the CPC (2.0) group. Meanwhile, the transcription of Nrf2/keap1 and antioxidant related genes, including CAT, GPx, GST, SOD1 and SOD2, was significantly elevated with the inclusion of CPC. In addition, the inclusion of CPC improved the non-specific immunity of largemouth bass. The activity of serum lysozyme was significantly elevated in the CPC (2.0) group, while the transcription of RelA and pro-inflammatory factors, including TNF-α and IL-1β, was inhibited with the inclusion of CPC. Meanwhile, related genes potentially linked to RelA, including TLR2 and p38 MAPK, were detected that their relative expression was significantly inhibited with the inclusion of CPC. The current findings indicated that the inclusion of 2% CPC improved the antioxidant capacity, non-specific immunity and disease resistance of juvenile largemouth bass, and suggested that 2% CPC as a functional additive could be applied to the diet of juvenile largemouth bass in aquaculture practice.

Yeast cell surface displaying VP28 antigen and its potential application for shrimp farming

VP28 is an envelope protein of White Spot Syndrome Virus (WSSV), which has been shown in previous studies to induce a high immune response in shrimp. VP28 has been produced in some host systems such as Escherichia coli, Bacillus subtilis, and Pichia pastoris as free protein. Here we showed a new strategy of anchoring VP28 on the Saccharomyces cerevisiae yeast surface and using the yeast cell extract combined with probiotic as an oral vaccine for shrimp farming. We have successfully constructed a recombinant yeast cell capable of expressing VP28 on the cell surface. The feeding diet combined with VP28 anchored yeast cell extract provided significant assurance to Litopenaeus vannamei, challenged by WSSV, resulting in a relative percent survival (RPS) of 87.10 ± 2.15%. Interestingly, the utilization of VP28 anchored yeast cell extract could enhance the efficiency of probiotic strains like Lactobacillus and Bacillus on shrimp farming. The results in both laboratory scales and field trials using extract of VP28 displaying Saccharomyces showed a growth-promoting effect in shrimp, assessed through average shrimp weight. Taken together, our results in this study demonstrated a new successful strategy of using yeast cell surface as a tool to produce VP28-based oral vaccine for shrimp aquaculture. KEY POINTS: • A new strategy of using VP28 antigen as anchored protein on S. cerevisiae yeast cell surface (S. cerevisiae::VP28) • The utilization of VP28 antigen and yeast as S. cerevisiae::VP28 extract enhanced potential protection of Litopenaeus vannamei against White Spot Syndrome Virus (RPS 87.10%) • The use of S. cerevisiae::VP28 extract increased efficiency of probiotic on shrimp growth-promoting effect either lab-scale or field trial.

Effects of Synechococcus sp. PCC 7942 harboring vp19, vp28, and vp (19 + 28) on the survival and immune response of Litopenaeus vannamei infected WSSV

This study aimed to assess the effect of oral administration of Synechococcus sp. PCC 7942 harboring vp19, vp28, and vp(19 + 28)against infection by white spot syndrome virus (WSSV) on juveniles of Litopenaeus vannamei. L. vannamei was orally administrated by feeding with different mutants of Synechococcus for 10 days, and then challenged with WSSV. The cumulative mortality of vp19, vp28, vp (19 + 28) groups was lower than that of the positive control group (57.8%, 62.2%, 71.1%, respectively); vp (19 + 28) group had a better protection rate than vp19 and vp28 groups. The analysis of shrimp immunological parameters showed that, after WSSV injection, the activity of superoxide dismutase, phenol oxidase, catalase, and lysozyme in the hepatopancreas of vp19, vp28, and vp (19 + 28) groups was higher than in the positive group; at the same time, growth performances of L. vannamei of experimental groups were better than control groups. Results showed that the Synechococcus mutants harboring vp19, vp28, and vp (19 + 28) could be used both as drug and feed to also enhance the defensive ability of juvenile shrimp against WSSV infection by increasing the activity of immune related enzymes.

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.

What vaccination studies tell us about immunological memory within the innate immune system of cultured shrimp and crayfish

The possibility of immunological memory in invertebrates is a topic that has recently attracted a lot of attention. Today, even vertebrates are known to exhibit innate immune responses that show memory-like properties, and since these responses are triggered by cells that are involved in the innate immune system, it seems that immune specificity and immune memory do not necessarily require the presence of B cells and T cells after all. This kind of immune response has been called "immune priming" or "trained immunity". In this report, we review recent observations and our current understanding of immunological memory within the innate immune system in cultured shrimp and crayfish after vaccination with live vaccine, killed vaccine and subunit vaccines. We also discuss the possible mechanisms involved in this immune response.

Biological Containment of Genetically Modified Bacillus subtilis

Genetic manipulation of bacterial spores of the genus Bacillus has shown potential for vaccination and for delivery of drugs or enzymes. Remarkably, proteins displayed on the spore surface retain activity and generally are not degraded. The heat stability of spores, coupled with their desiccation resistance, makes them suitable for delivery to humans or to animals by the oral route. Despite these attributes, one regulatory obstacle has remained regarding the fate of recombinant spores shed into the environment as viable spores. We have addressed the biological containment of GMO spores by utilizing the concept of a thymineless death, a phenomenon first reported 6 decades ago. Using Bacillus subtilis, we have inserted chimeric genes in the two thymidylate synthase genes, thyA and thyB, using a two-step process. Insertion is made first at thyA and then at thyB whereby resistance to trimethoprim enables selection of recombinants. Importantly, this method requires introduction of no new antibiotic resistance genes. Recombinant spores have a strict dependence on thymine (or thymidine), and in its absence cells lyse and die. Insertions are stable with no evidence for suppression or reversion. Using this system, we have successfully created a number of spore vaccines as well as spores displaying active enzymes.IMPORTANCE Genetic manipulation of bacterial spores offers a number of exciting possibilities for public and animal health, including their use as heat-stable vehicles for delivering vaccines or enzymes. Despite this, one remaining problem is the fate of recombinant spores released into the environment where they could survive in a dormant form indefinitely. We describe a solution whereby, following genetic manipulation, the bacterium is rendered dependent on thymine. As a consequence, spores if released would produce bacteria unable to survive, and they would exhibit a thymineless death due to rapid cessation of metabolism. The method we describe has been validated using a number of exemplars and solves a critical problem for containing spores of GMOs in the environment.

The promotion of cytoskeleton integration and redox in the haemocyte of shrimp Litopenaeus vannamei after the successive stimulation of recombinant VP28

VP28 protein has been reported to work as a "vaccine" to protect the host from white spot syndrome, but the detailed mechanism of vaccination with VP28 protein in shrimp is still far from well understood. In the present study, whole transcriptomes of shrimp haemocytes were sequenced using the SOLiD4 platform after the successive VP28 stimulation. Eight single-end fragment libraries were constructed and sequenced in the four groups including the VP28-VP28, PBS-VP28, PBS-PBS and BLANK group, and there were 243,949,667 single-end reads with length of 50bp obtained totally, with 14,800 genes further identified. After reads mapping and transcript assembling, 1027, 1539, 1158, 1091 and 1300 genes in five differentially expressed gene lists were obtained in the comparison of VP28-VP28 versus PBS-VP28, VP28-VP28 versus PBS-PBS, VP28-VP28 versus BLANK, PBS-VP28 versus PBS-PBS and PBS-VP28 versus BLANK, respectively. There were 555 differentially expressed genes responsive to the single VP28 stimulation after grouping the PBS-VP28_BLANK and PBS-VP28_PBS-PBS gene lists, and 269 ones responsive to the successive VP28 stimulation after grouping the VP28-VP28_BLANK, VP28-VP28_PBS-PBS and VP28-VP28_PBS-VP28 gene lists. In the GO enrichment analysis of the genes responsive to the single VP28 stimulation, five immune-related GO terms were observed among 14 increased terms, which included defense response to bacterium, response to stimulus, disruption of cells of other organism, killing of cells of other organism and response to bacterium. It was worth noting that the GO terms, response to stimulus and response to stress, were the most common annotation ones which accounted 28.7% and 18.8% of the total differently expressed genes, respectively. For the genes responsive to the successive VP28 stimulation, terms including actin filament-based movement and myosin heavy chain binding were mostly enriched in the Biological Process and Molecular Function category, respectively. In the Cellular Component category, the enriched GO terms were myosin VII complex, myosin V complex, myosin VI complex and myosin II complex. Furthermore, the most abundant GO term was oxidation-reduction process, followed by single-organism transport, neurogenesis and translation for 214 genes only responsive to successive VP28 stimulation. These results collectively indicated that the successive VP28 stimulation could modulate cytoskeleton integration and redox to promote the phagocytosis activity of shrimp haemocytes, which might protect effectively for shrimp against WSSV infection.

Cloning and enhancing production of a detergent- and organic-solvent-resistant nattokinase from Bacillus subtilis VTCC-DVN-12-01 by using an eight-protease-gene-deficient Bacillus subtilis WB800

Background

Nattokinases/Subtilisins (EC 3.4.21.62) belong to the second large family of serine proteases, which gain significant attention and play important role in many biotechnology processes. Thus, a number of nattokinases/subtilisins from various Bacillus species, especially from B. subtilis strains, extensively have been investigated to understand their biochemical and physical properties as well as to improve the production for industrial application. The purpose of this study was to clone a nattokinase gene from Bacillus subtilis strain VTCC-DVN-12-01, enhance its production in B. subtilis WB800, which is deficient in eight extracellular proteases and characterize its physicochemical properties for potential application in organic synthesis and detergent production.

Results

A gene coding for the nattokinase (Nk) from B. subtilis strain VTCC-DVN-12-01 consisted of an ORF of 1146 nucleotides, encoding a pre-pro-protein enzyme (30-aa pre-signal peptide, 76-aa pro-peptide and 275-aa mature protein with a predicted molecular mass of 27.7 kDa and pI 6.6). The nattokinase showed 98-99% identity with other nattokinases/subtilisins from B. subtilis strains in GenBank. Nk was expressed in B. subtilis WB800 under the control of acoA promoter at a high level of 600 mg protein per liter culture medium which is highest yield of proteins expressed in any extracellular-protease-deficient B. subtilis system till date. Nk was purified to homogeneity with 3.25 fold purification, a specific activity of 12.7 U/mg, and a recovery of 54.17%. The purified Nk was identified by MALDI-TOF mass spectrometry through three peptides, which showed 100% identity to corresponding peptides of the B. subtilis nattokinase (CAC41625). An optimal activity for Nk was observed at 65°C and pH 9. The nattokinase was stable at temperature up to 50°C and in pH range of 5–11 and retained more than 85% of its initial activity after incubation for 1 h. Mg²⁺ activated Nk up to 162% of its activity. The addition of Triton X-100, Tween 20, and Tween 80 showed an activation of Nk up to 141% of its initial activity but SDS strongly inhibited. The enzyme was highly resistant to organic solvents.

Conclusions

Our findings demonstrated that an eight-protease-gene-deficient Bacillus subtilis WB800 could overproduce the nattokinase from B. subtilis VTCC-DVN-12-01. Due to high resistance to detergents and organic solvents of this nattokinase, it could be potentially applied in organic synthesis and detergent production.

Host and virus protein interaction studies in understanding shrimp virus gene function

Protein-protein interaction studies have been widely used in several fields to characterize an unknown protein. This in turn helps to find out several pathways to understand a complex mechanism or discover a drug for treatment. Among the methods, yeast two-hybrid has widely been used in human, animal and plant research studies. This aspect of research has also been found useful in understanding the shrimp virus gene function. With respect to White spot syndrome virus, interaction studies have been applied to elucidate virus structure, understand the mode of entry of the virus, mechanism of virus replication and also to discover some of the host anti-viral proteins. Interaction studies on other shrimp viruses are scanty and only few reports available on Yellow head virus and Taura syndrome virus. All these findings are still in preliminary stage and lot more studies are necessary to have the clear picture. Protein interaction research on other shrimp viruses are still lacking. Considering all these, it appears that this field of research has a wide scope to understand the virulence mechanism of shrimp viruses where very little information is available till date.

Arabidopsis-derived shrimp viral-binding protein, PmRab7 can protect white spot syndrome virus infection in shrimp

White spot syndrome virus is currently the leading cause of production losses in the shrimp industry. Penaeus monodon Rab7 protein has been recognized as a viral-binding protein with an efficient protective effect against white spot syndrome infection. Plant-derived recombinant PmRab7 might serve as an alternative source for in-feed vaccination, considering the remarkable abilities of plant expression systems. PmRab7 was introduced into the Arabidopsis thaliana T87 genome. Arabidopsis-derived recombinant PmRab7 showed high binding activity against white spot syndrome virus and a viral envelope, VP28. The growth profile of Arabidopsis suspension culture expressing PmRab7 (ECR21# 35) resembled that of its counterpart. PmRab7 expression in ECR21# 35 reached its maximum level at 5 mg g(-1) dry weight in 12 days, which was higher than those previously reported in Escherichia coli and in Pichia. Co-injection of white spot syndrome virus and Arabidopsis crude extract containing PmRab7 in Litopenaeus vannamei showed an 87% increase in shrimp survival rate at 5 day after injection. In this study, we propose an alternative PmRab7 source with higher production yield, and cheaper culture media costs, that might serve the industry's need for an in-feed supplement against white spot syndrome infection.

A vector that expresses VP28 of WSSV can protect red swamp crayfish from white spot disease

White spot disease caused by white spot syndrome virus (WSSV) leads to devastating losses in shrimp farming. The WSSV envelope protein VP28, can be used as subunit vaccines that can efficiently protect shrimp against WSSV disease. However, the function of the envelope protein VP19 was not confirmed, some researches found that VP19 could protect shrimp against WSSV, and other reports found it no any protection. To detect the functions of VP28 and VP19 and find a method to prevent this disease in red swamp crayfish Procambarus clarkii, we constructed the plasmid vectors pIevp28 and pIevp19, which contains the ie1 promoter and coding region of vp28 or vp19 of WSSV, respectively. The results of quantitative real-time PCR and western blot showed that the injected vectors could transcribe corresponding mRNAs and translate to the protein VP28 or VP19 in the crayfish. The vp28 or vp19 signal was detected on the third day post injection, and maintained its expression for 30days. The mortality of the crayfish with pIevp28 showed obvious decline compared with the controls (pIe and PBS injection). However, pIevp19 seems did not affect the mortality of the crayfish compared with the controls. Furthermore, only VP28 was found tightly bound to the host haemocytes under immunocytochemistry. The results suggest that the VP28 protein might protect shrimp from the virus through competitive inhibition. We also found that oral administration of Escherichia coli with pIevp28 could protect crayfish from white spot disease, but the E. coli with pIevp19 was not. Therefore, we think that oral administration of bacteria with pIevp28 is a potentially easy therapeutic way against white spot disease in aquaculture.

Production of human papillomavirus type 33 L1 major capsid protein and virus-like particles from Bacillus subtilis to develop a prophylactic vaccine against cervical cancer

We developed a bacterial expression system to produce human papillomavirus (HPV) type 33 L1 major capsid protein and virus-like particles from a recombinant Bacillus subtilis strain. For the first time, we have isolated self-assembled virus-like particles (VLPs) of HPV type 33 from B. subtilis, a strain generally recognized as safe (GRAS). The gene encoding the major capsid protein L1 of HPV type 33 was amplified from viral DNA isolated from a Korean patient and expressed in B. subtilis; a xylose-induction system was used to control gene activity. HPV33 L1 protein was partially purified by 40% (w/v) sucrose cushion centrifugation and strong cation exchange column chromatography. Eluted samples exhibited immunosignaling in fractions of 0.5-1.0 M NaCl. The HPV33 L1 protein was shown to be approximately 56 kDa in size by SDS-PAGE and Western blotting; recovery and purity were quantified by indirect immuno-ELISA assay. The final yield and purity were approximately 20.4% and 10.3%, respectively. Transmission electron microscopic analysis of fractions immunoactive by ELISA revealed that the L1 protein formed self-assembled VLPs with a diameter of approximately 20-40 nm. Humoral and cellular immune responses provoked by the B. subtilis/HPV33 L1 strain were approximately 100- and 3-fold higher than those of the empty B. subtilis strain as a negative control, respectively. Development of a VLP production and delivery system using B. subtilis will be helpful, in that the vaccine may be convenient production as an antigen delivery system. VLPs thus produced will be safer for human use than those purified from Gram-negative strains such as Escherichia coli. Also, use of B. subtilis as a host may aid in the development of either live or whole cell vaccines administered by antigen delivery system.

Surface-displayed VP28 on Bacillus subtilis spores induce protection against white spot syndrome virus in crayfish by oral administration

AIM

Surface-displayed heterologous antigens on Bacillus subtilis spores can induce the vertebrate animals tested to generate local and systematic immune response through oral immunization. Here, the protection potential of the recombinant spores displaying the VP28 protein of white spot syndrome virus (WSSV) was investigated in the invertebrate crayfish (Cambarus clarkii).

METHODS AND RESULTS

The VP28 protein was successfully displayed on the surfaces of B. subtilis spores using CotB or CotC as a fusion partner. Crayfish were administrated orally by feeding the feed pellets coated with B. subtilis spores for 7 days and immediately followed by WSSV challenge. Oral administration of either spores expressing CotB-VP28 or CotC-VP28 resulted in significantly higher relative survival rates of 37.9 and 44.8% compared with the crayfish orally administrated with the spores nonexpressing VP28 (10.3% relative survival rate). When challenges were separately conducted at 7 and 21 days after oral administration, the relative survival rates increased to 46.4 and 50% at 7 days post-oral administration, but decreased to 30 and 33.3% at 21 days after oral administration.

CONCLUSION

These evidences indicate that the surface-displayed VP28 on B. subtilis spore could induce protection of crayfish against WSSV via oral administration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report to use the spore surface display system to deliver orally a heterologous antigen in an aquatic invertebrate animal, crayfish. The results presented here suggest that the spore-displayed VP28 might be suitable for an oral booster vaccine on prevention of WSSV infection in shrimp farming.

Immune responses to the oral administration of recombinant Bacillus subtilis expressing multi-epitopes of foot-and-mouth disease virus and a cholera toxin B subunit

Bacillus subtilis has been engineered successfully to express heterologous antigens for use as a vaccine vehicle that can elicit mucosal and systemic immunity response. In this study, a recombinant B. subtilis expressing the B subunit of cholera toxin (CT-B) and an epitope box constituted with antigen sites from foot-and-mouth disease virus (FMDV) type Asia 1 was constructed and named 1A751/CTB-TEpiAs. Its capability to induce mucosal, humoral, and cellular responses in mice and guinea pigs was evaluated after oral administration with vegetative cells of 1A751/CTB-TEpiAs. In addition, its capability to protect guinea pigs against homologous virus challenge was examined. All animals were given booster vaccination at day 21 after initial inoculation and guinea pigs were challenged 3 weeks after booster vaccination. The control groups were inoculated with a commercial vaccine or administered orally with 1A751/pBC38C or an oral buffer. All animals vaccinated with 1A751/CTB-TEpiAs developed specific anti-FMDV IgA in lung and gut lavage fluid, serum ELISA antibody, neutralizing antibody as well as T lymphocyte proliferation, and IFN-γ secretory responses. Three of the five guinea pigs vaccinated with 1A751/CTB-TEpiAs were protected completely from the viral challenge. The results demonstrate the potential viability of a B. subtilis-based recombinant vaccine for the control and prevention of FMDV infections.

Antiviral immunity in crustaceans

Viral diseases of shrimp have caused negative effects on the economy in several countries in Asia, South America and America, where they have numerous shrimp culture industries. The studies on the immunity of shrimp and other crustaceans have mainly focused on general aspects of immunity and as a consequence little is known about the antiviral responses in crustaceans. The aim of this review is to update recent knowledge of innate immunity against viral infections in crustaceans. Several antiviral molecules have been isolated and characterized recently from decapods. Characterization and identification of these molecules might provide a promising strategy for protection and treatment of these viral diseases. In addition dsRNA-induced antiviral immunity is also included.

Protection of Procambarus clarkii against white spot syndrome virus using inactivated WSSV

White spot syndrome virus (WSSV) is a highly pathogenic and prevalent virus infecting shrimp and other crustaceans. The potentiality of binary ethylenimine (BEI)-inactivated WSSV against WSSV in crayfish, Procambarus clarkii, was investigated in this study. Efficacy of BEI-inactivated WSSV was tested by vaccination trials followed by challenge of crayfish with WSSV. The crayfish injected with BEI-inactivated WSSV showed a better survival (P<0.05) to WSSV on the 7th and 21st day post-vaccination (dpv) compared to the control. Calculated relative percent survival (RPS) values were 77% and 60% on the 7th and 21st dpv for 2mM BEI-inactivated WSSV, and 63%, 30% on 7th and 21st dpv for 3mM BEI-inactivated WSSV. However, heat-inactivated WSSV did not provide protection from WSSV even on 7th dpv. In the inactivation process WSSV especially their envelope proteins maybe changed as happened to 3mM BEI and heat-inactivated WSSV particles. These results indicate the protective efficacy of BEI-inactivated WSSV lies on the integrity of envelope proteins of WSSV and the possibility of BEI-inactivated WSSV to protect P. clarkii from WSSV.