The white spot syndrome virus DNA genome sequence

Cellular entry of white spot syndrome virus and antiviral immunity mediated by cellular receptors in crustaceans

Enveloped virus usually utilizes the receptor-mediated multiple endocytic routes to enter permissive host cells for successful infection. Cellular receptors are cell surface molecules, either by helping viral attachment to cell surface followed by internalization or by triggering antiviral immunity, participate in the viral-host interaction. White spot syndrome virus (WSSV), the most lethally viral pathogen with envelope and double strand DNA genome in crustacean farming, including shrimp and crayfish, has been recently found to recruit various endocytic routes for cellular entry into host cells. Meanwhile, other than the typical pattern recognition receptors for recognition of WSSV, more and more putative cellular receptors have lately been characterized to facilitate or inhibit WSSV entry. In this review, recent findings on the endocytosis-dependent WSSV entry, viral entry mediated by putative cellular receptors, the molecular interplay between WSSV and cellular receptors, and the following anti-WSSV immunity are summarized and discussed, which may provide us a better understanding of the WSSV pathogenesis and further possible antiviral control of white spot disease in crustacean farming.

Molecular variability and genetic structure of white spot syndrome virus strains from northwest Mexico based on the analysis of genomes

White spot syndrome virus (WSSV) has a ∼300 kb double-stranded DNA genome. It originated in China, spread rapidly through shrimp farms in Asia, and subsequently to America. This study determined complete genome sequences for nine historic WSSV strains isolated from Pacific white shrimp (Litopenaeus vannamei) captured in farm ponds in northwest Mexico (Sinaloa and Nayarit). Genomic DNA was captured by an amplification method using overlapping long-range PCR and sequencing by Ion Torrent-PGM. Complete genome sequences were assembled (length range 255-290 kb) and comparative genome analysis with WSSV strains revealed substantial deletions (3 and 10 kb in two regions) in seven strains, with two strains differing from the rest. Phylogenetic analysis identified that the WSSV strains from the northern area of the state of Sinaloa clustered with strains from China (LC1, LC10, DVI) and Korea (ACF2, ACF4), while those from the southern region of the state of Nayarit (AC1 and JP) differed from both of those and from strains found in Taiwan and Thailand. Our data offer insights into the diversity of the WSSV genome in one country and their divergent origin, suggest that it entered Mexico via multiple routes and that specific genome regions can accommodate substantial deletions without compromising viability.

Temporal changes in transcriptome profile provide insights of White Spot Syndrome Virus infection in Litopenaeus vannamei

Shrimp aquaculture is severely affected by WSSV. Despite an increasing effort to understand host/virus interaction by characterizing changes in gene expression (GE) following WSSV infection, the majority of published studies have focussed on a single time-point, providing limited insight on the development of host-pathogen interaction over the infection cycle. Using RNA-seq, we contrasted GE in gills of Litopenaeus vannamei at 1.5, 18 and 56 hours-post-infection (hpi), between WSSV-challenged and control shrimps. Time course analysis revealed 5097 differentially expressed genes: 63 DEGs were viral genes and their expression in WSSV group either peaked at 18 hpi (and decreased at 56 hpi) or increased linearly up to 56 hpi, suggesting a different role played by these genes during the course of infection. The remaining DEGs showed that WSSV altered the expression of metabolic, immune, apoptotic and cytoskeletal genes and was able to inhibit NF-κB and JAK/STAT pathways. Interestingly, GE changes were not consistent through the course of infection but were dynamic with time, suggesting the complexity of host-pathogen interaction. These data offer novel insights into the cellular functions that are affected during the course of infection and ultimately provide a valuable resource towards our understanding of the host-pathogen dynamics and its variation with time.

Role of Clathrin Assembly Protein-2 Beta Subunit during White Spot Syndrome Virus Infection in Black Tiger Shrimp Penaeus monodon

White spot syndrome virus (WSSV) is one of the most lethal viruses severely affecting shrimp industry. This disease can cause 100% mortality of farmed shrimp within a week. This work aims to characterize clathrin assembly proteins in Penaeus monodon and investigate their roles in WSSV entry. In general, clathrin assembly proteins form complexes with specific receptors and clathrins, leading to clathrin-mediated endocytosis. Adaptor protein 2 (AP-2), which is responsible for endocytosis at plasma membrane, consists of four subunits including α, β2, μ2 and σ2. Knockdown of clathrin coat AP17, or σ subunit of AP-2 dramatically reduced WSSV infectivity. Similar results were observed, when shrimp were pre-treated with chlorpromazine (CPZ), an inhibitor of clathrin-dependent endocytosis. The complete open reading frames of AP-2β and μ subunits of P. monodon are reported. PmAP-2 β was up-regulated about 4-fold at 6 and 36 h post-WSSV infection. Knockdown of PmAP-2β delayed shrimp mortality during WSSV infection, of which WSSV intermediate early 1 gene expression was also down-regulated. Immunogold-labelling and transmission electron microscopy revealed that PmAP-2β co-localized with WSSV particles at plasma membrane. In addition, PmAP-2β-silencing significantly affected the expression levels of PmSTAT, PmDOME, PmDorsal and ALFPm3 during WSSV infection. It is possible that PmAP-2β is associated with the JAK/STAT and the Toll pathway.

Hypoxia inducible factor -1 regulates WSSV-induced glycolytic genes in the white shrimp Litopenaeus vannamei

Hypoxia-inducible factor -1 (HIF-1) is a transcriptional factor that regulates the expression of several glycolytic genes. The white spot syndrome virus (WSSV) induces a shift in glycolysis that favors viral replication in white shrimp Litopenaeus vannamei. HIF-1 is related to the pathogenesis of the WSSV infection through the induction of metabolic changes in infected white shrimp. Although the WSSV infection is associated with metabolic changes, the role of HIF-1 on key glycolytic genes during the WSSV infection has not been examined. In this work, we evaluated the effect of HIF-1α silencing on expression and activity of glycolytic enzymes (Hexokinase-HK, phosphofructokinase-PFK and pyruvate kinase-PK) along with the glucose transporter 1 (Glut1), regulatory enzymes (glucose-6-phosphate dehydrogenase-G6PDH and pyruvate dehydrogenase-PDH), and metabolic intermediates of glycolysis (glucose-6-phosphate-G6P and pyruvate). The expression of Glut1 increased in each tissue evaluated after WSSV infection, while HK, PFK and PK gene expression and enzyme activities increased in a tissue-specific manner. G6PDH activity increased during WSSV infection, and its substrate G6P decreased, while PDH activity decreased and its substrate pyruvate increased. Silencing of HIF-1α blocked the WSSV-induced Glut1 and glycolytic genes upregulation and enzyme activity in a tissue-specific manner. We conclude that HIF-1 regulates the WSSV-induced glycolysis through induction of glycolytic genes contributing to glucose metabolism in tissues of infected shrimp. Also, the inhibition, and activation of regulatory genes are likely to decrease the availability of the raw materials essential for WSSV replication and increase oxidative metabolism.

Global distribution of white spot syndrome virus genotypes determined using a novel genotyping assay

White spot disease, caused by infection with white spot syndrome virus (WSSV), is a serious panzootic affecting prawn aquaculture. The disease has spread rapidly around the prawn-culturing regions of the world through a number of previously identified mechanisms. The ability to distinguish and trace strains of WSSV is of great benefit to identify, and then limit, the translocation routes of the disease. Here, we describe a novel genotyping method using 34 short tandem repeat regions of the viral genome concurrently. This technique is highly sensitive to strain differences when compared to previous methods. The efficacy of the described method is demonstrated by testing WSSV isolates from around the globe, showing regional genotypic differences. The differences in the genotypes were used to create a global minimum spanning network, and in most cases the observed relationships were substantiated with verification of transboundary movement. This novel panel of STR markers will provide a valuable epidemiological tool for white spot disease. We have applied this to an outbreak of the disease in Queensland, Australia, that occurred in 2016. While the results indicate that the source of this outbreak currently remains cryptic, the analyses have provided valuable insights with which to further study the origins of the strains involved.

VP19 is important for the envelope coating of white spot syndrome virus

VP19 is a major envelope protein of white spot syndrome virus (WSSV), an important pathogen of farmed shrimp. However, the exact function of VP19 in WSSV assembly and infection is unknown. To understand the function of VP19, the gene was knocked down by RNA interference. We found that the dsRNA specific for vp19 gene dramatically reduced the replication of WSSV genomic DNA in infected animals. Further investigation by transmission electron microscopy showed that inhibition of VP19 prevented envelope coating of progeny virions, resulting in a high amount of immature virus particles without outer layer (envelope) in the host cells. This finding was further confirmed by SDS-PAGE analysis, which showed the loss of VP19 and other envelope proteins from the improperly assembled virions. These results suggest that VP19 is essential for WSSV envelope coating.

Characterization of putative proteins encoded by variable ORFs in white spot syndrome virus genome

Background

White Spot Syndrome Virus (WSSV) is an enveloped double-stranded DNA virus which causes mortality of several species of shrimp, being considered one of the main pathogens that affects global shrimp farming. This virus presents a complex genome of ~ 300 kb and viral isolates that present genomes with great identity. Despite this conservation, some variable regions in the WSSV genome occur in coding regions, and these putative proteins may have some relationship with viral adaptation and virulence mechanisms. Until now, the functions of these proteins were little studied. In this work, sequences and putative proteins encoded by WSSV variable regions were characterized in silico.

Results

The in silico approach enabled determining the variability of some sequences, as well as the identification of some domains resembling the Formin homology 2, RNA recognition motif, Xeroderma pigmentosum group D repair helicase, Hemagglutinin and Ankyrin motif. The information obtained from the sequences and the analysis of secondary and tertiary structure models allow to infer that some of these proteins possibly have functions related to protein modulation/degradation, intracellular transport, recombination and endosome fusion events.

Conclusions

The bioinformatics approaches were efficient in generating three-dimensional models and to identify domains, thereby enabling to propose possible functions for the putative polypeptides produced by the ORFs wsv129, wsv178, wsv249, wsv463a, wsv477, wsv479, wsv492, and wsv497.

Electronic supplementary material

The online version of this article (10.1186/s12900-019-0106-y) contains supplementary material, which is available to authorized users.

Transcriptome of white shrimp Litopenaeus vannamei induced with rapamycin reveals the role of autophagy in shrimp immunity

Autophagy plays a vital role in innate and adaptive immunity against invading microorganisms, such as virus and bacteria. However, the mechanism underlying autophagy in shrimp is still limited. In our study, we challenged white shrimp L. vannamei with rapamycin to induce autophagy and employed Solexa/Illumina high-throughput RNA-seq method to examine the differences of transcriptome from gills of shrimps treated with or without rapamycin. More than 22.64 Gb raw data were produced, which were assembled into 62, 503 unigenes, with 14,126 unigenes over 1 kb in length. We then performed differential expression analysis and identified a total of 3050 differentially expressed genes (DEGs). Among them, 1456 were upregulated and 1594 were downregulated. We further annotated DEGs by matching against non-redundant protein sequence (Nr), Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes (KEGG), Clusters of Orthologous Groups of proteins (COG), euKaryotic Orthologous Groups (KOG), Gene ontology (GO), and Pfam databases. The assembled and annotated DEGs will facilitate our understanding of the molecular mechanism underlying autophagy and promote the studies on the role of autophagy in innate immunity of L. vannamei and other crustaceans.

Alternative PCR primers for genotyping of Brazilian WSSV isolates

White spot syndrome virus (WSSV) is one of the major challenges faced by global shrimp farming in recent decades. The characterization of WSSV genetic variability has been used to determine viral dispersion and is a promising method to determine the association between genotype and virulence. The major variable regions that have been used as markers to differentiate the WSSV genomes include the VNTR loci inside ORF94, ORF75, ORF125, and insertions/deletions interspersing ORF14/15 and ORF23/24. The primers used to amplify these regions were described at least 10 years ago, but some of them do not work efficiently to identify new WSSV variants. The objective of this work was to develop improved PCR primers for WSSV genotyping based on sequence alignments that include new sequences described in recent years. We validated these new primers in a pilot study to verify the genetic variability of the WSSV in Rio Grande do Norte state (northeast Brazil), and efficiency was compared to that of other previously described primers. We confirmed that the primers we developed were more efficient for genotype Brazilian WSSV isolates, enabling us to genotype a larger number of samples. In addition, our results also introduce new data about the genetic characterization of the WSSV isolates that occur in the northeastern region of Brazil.

Identification and characterization of novel double zinc fingers encoded by putative proteins in genome of white spot syndrome virus

White spot syndrome virus (WSSV), is a major viral pathogen affecting the shrimp culture industry worldwide. Studies in understanding the mechanisms of WSSV pathogenicity has led to the identification of The Really Interesting New Gene (RING) finger domains in WSSV encoded proteins that have been shown to function as E3 ligase modulating the host-ubiquitin pathway. In this study, we report two proteins encoded by the WSSV genome to harbor a double zinc finger domain, one each in its N- and C-terminal region. Sequence and structural analysis of the two domains showed the N- and C-terminal domains to be similar to known RING1 and RING2 domains of eukaryotic RBR (RING-between-RING) ligases respectively. This is the first report wherein genes within WSSV are shown to encode for double RING domains, which could pave way in understanding further, the function of these proteins and their role in the pathogenic mechanisms of the virus.

Quantitative analysis of the dose-response of white spot syndrome virus in shrimp

White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose-response by a combination of experiments, modelling and meta-analysis. We performed dose-response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models-differing in whether they incorporated heterogeneous host susceptibility to the virus or not-were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose-response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose-response, which can elucidate the most basic virus-host interactions and help to avoid underestimating WSSV infection at low virus doses.

Silencing of HIF-1 in WSSV-infected white shrimp: Effect on viral load and antioxidant enzymes

Hypoxia inducible factor-1 (HIF-1) is a transcriptional factor that induces genes involved in glucose metabolism. HIF-1 is formed by a regulatory α-subunit (HIF-1α) and a constitutive β-subunit (HIF-1β). The white spot syndrome virus (WSSV) induces a shift in glucose metabolism and oxidative stress. HIF-1α is associated with the induction of metabolic changes in tissues of WSSV-infected shrimp. However, the contributions of HIF-1 to viral load and antioxidant responses in WSSV-infected shrimp have been not examined. In this study, the effect of HIF-1 silencing on viral load and the expression and activity of antioxidant enzymes (superoxide dismutase-SOD, glutathione S-transferase-GST, and catalase) along with oxidative damage (lipid peroxidation and protein carbonyl) in tissues of white shrimp infected with the WSSV were studied. The viral load increased in hepatopancreas and muscle after WSSV infection, and the accumulative mortality was of 100% at 72 h post-infection. The expression and activity of SOD, catalase, and GST decreased in each tissue evaluated after WSSV infection. Protein carbonyl concentrations increased in each tissue after WSSV infection, while lipid peroxidation increased in hepatopancreas, but not in muscle. Silencing of HIF-1α decreased the WSSV viral load in hepatopancreas and muscle of infected shrimp along with shrimp mortality. Silencing of HIF-1α ameliorated the antioxidant response in a tissue-specific manner, which translated to a decrease in oxidative damage. These results suggest that HIF-1 is essential for restoring the antioxidant response, which counters the oxidative injury associated with WSSV infection.

Identification of Litopenaeus vannamei BiP as a novel cellular attachment protein for white spot syndrome virus by using a biotinylation based affinity chromatography method

White spot syndrome virus (WSSV) is a dangerous threat to shrimp farming that also attacks a wide range of crustaceans. Knowledge of the surface protein-protein interactions between the pathogen and host is very crucial to unraveling the molecular pathogenesis mechanisms of WSSV. In this study, LvBiP (Litopenaeus vannamei immunoglobulin heavy-chain-binding protein) was identified as a novel WSSV binding protein of L. vannamei by a biotinylation based affinity chromatography method. By using pull-down and ELISA assays, the binding of recombinant LvBiP to WSSV was proved to be specific and ATP- dependent. The interaction was also confirmed by the result of co-immunoprecipitation assay. Immunofluorescence studies revealed the co-localization of LvBiP with WSSV on the cell surface of shrimp haemocytes. Additionally, LvBiP is likely to play an important role in WSSV infection. Treatment of gill cellular membrane proteins (CMPs) with purified rLvBiP and antibody that specifically recognizes LvBiP, led to a significant reduction in the binding of WSSV to gill CMPs. In the in vivo neutralization assay, rLvBiP and anti-LvBiP polyclonal antibody partially blocked the infection of WSSV. Taken together, the results indicate that LvBiP, a molecular chaperon of the HSP70 family, is a novel host factor involved at the step of attachment of the WSSV to the host cells and a potential candidate of therapeutic target.

A transcriptome study on Macrobrachium nipponense hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is one of the most devastating pathogens of cultured shrimp, responsible for massive loss of its commercial products worldwide. The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China and adult prawns can be infected by WSSV. However, the molecular mechanisms of the host pathogen interaction remain unknown. There is an urgent need to learn the host pathogen interaction between M. nipponense and WSSV which will be able to offer a solution in controlling the spread of WSSV. Next Generation Sequencing (NGS) was used in this study to determin the transcriptome differences by the comparison of control and WSSV-challenged moribund samples, control and WSSV-challenged survived samples of hepatopancreas in M. nipponense. A total of 64,049 predicted unigenes were obtained and classified into 63 functional groups. Approximately, 4,311 differential expression genes were identified with 3,308 genes were up-regulated when comparing the survived samples with the control. In the comparison of moribund samples with control, 1,960 differential expression genes were identified with 764 genes were up-regulated. In the contrast of two comparison libraries, 300 mutual DEGs with 95 up-regulated genes and 205 down-regulated genes. All the DEGs were performed GO and KEGG analysis, overall a total of 85 immune-related genes were obtained and these gene were groups into 13 functions and 4 KEGG pathways, such as protease inhibitors, heat shock proteins, oxidative stress, pathogen recognition immune receptors, PI3K/AKT/mTOR pathway, MAPK signaling pathway and Ubiquitin Proteasome Pathway. Ten genes that valuable in immune responses against WSSV were selected from those DEGs to furture discuss the response of host to WSSV. Results from this study contribute to a better understanding of the immune response of M. nipponense to WSSV, provide information for identifying novel genes in the absence of genome of M. nipponense. Furthermore, large number of transcripts obtained from this study could provide a strong basis for future genomic research on M. nipponense.

A new strain of white spot syndrome virus affecting Litopenaeus vannamei in Indian shrimp farms

White spot syndrome virus (WSSV)-infected shrimp samples collected from grow-out ponds located at Nellore, Andhra Pradesh, India, showed WSSV negative and positive by PCR using primer sets specific to ORF119 and VP28 gene of WSSV, respectively. This indicated the deletion of genetic fragments in the genome of WSSV. The WSSV isolate along with lab strain of WSSV was subjected to next-generation sequencing. The sequence analysis revealed a deletion of 13,170 bp at five positions in the genome of WSSV-NS (new strain) relative to WSSV-TH and WSSV-LS (lab strain). The PCR analysis using the ORF's specific primer sets revealed the complete deletion of 10 ORFs in the genome of WSSV-NS strain. The primer set was designed based on sequence covering ORF161/162/163 to amplify a product of 2,748 bp for WSSV-LS and 402 bp for WSSV-NS. Our surveillance programme carried out since 2002 revealed the replacement of WSSV-LS by WSSV-NS in Indian shrimp culture system.

Draft Genome Sequence of a White Spot Syndrome Virus Isolate Obtained in Ecuador

White spot syndrome virus (WSSV) is the most devastating viral disease affecting cultivated shrimp around the world. Currently, there is no reported genetic information on WSSV affecting Penaeus vannamei in Ecuador.

White spot syndrome virus (WSSV) is the most devastating viral disease affecting cultivated shrimp around the world. Currently, there is no reported genetic information on WSSV affecting Penaeus vannamei in Ecuador. Therefore, we determined the genome of a WSSV isolate from shrimp and compared it with the genomes of isolates from other geographical locations.

Shrimp hemocyte homeostasis-associated protein (PmHHAP) interacts with WSSV134 to control apoptosis in white spot syndrome virus infection

Hemocyte homeostasis-associated protein (PmHHAP) was first identified as a viral-responsive gene, due to a high upregulation in transcription following white spot syndrome virus (WSSV) infection. Functional studies using RNA interference have suggested that PmHHAP is involved in hemocyte homeostasis by controlling apoptosis during WSSV infection. In this study, the role of PmHHAP in host-viral interactions was further investigated. Yeast two-hybrid assay and co-immunoprecipitation revealed that PmHHAP binds to an anti-apoptosis protein, WSSV134. The viral protein WSSV134 is a late protein of WSSV, expressed 24 h post infection (hpi). Gene silencing of WSSV134 in WSSV-infected shrimp resulted in a reduction of the expression level of the viral replication marker genes VP28, wsv477, and ie-1, which suggests that WSSV134 is likely involved in viral propagation. However, co-silencing of PmHHAP and WSSV134 counteracted the effects on WSSV infection, which implies the importance of the host-pathogen interaction between PmHHAP and WSSV134 in WSSV infection. In addition, caspase 3/7 activity was noticeably induced in the PmHHAP and WSSV134 co-silenced shrimp upon WSSV infection. Moreover, PmHHAP and WSSV134 inhibited caspase-induced activation of PmCasp in vitro in a non-competitive manner. Taken together, these results suggest that PmHHAP and WSSV134 play a role in the host-pathogen interaction and work concordantly to control apoptosis in WSSV infection.

Regulation of lactate dehydrogenase in response to WSSV infection in the shrimp Litopenaeus vannamei

Lactate dehydrogenase (LDH) is key for anaerobic glycolysis. LDH is induced by the hypoxia inducible factor -1 (HIF-1). HIF-1 induces genes involved in glucose metabolism and regulates cellular oxygen homeostasis. HIF-1 is formed by a regulatory α-subunit (HIF-1α) and a constitutive β-subunit (HIF-1β). The white spot syndrome virus (WSSV) induces anaerobic glycolysis in shrimp hemocytes, associated with lactate accumulation. Although infection and lactate production are associated, the LDH role in WSSV-infected shrimp has not been examined. In this work, the effects of HIF-1 silencing on the expression of two LDH subunits (LDHvan-1 and LDHvan-2) in shrimp infected with the WSSV were studied. HIF-1α transcripts increased in gills, hepatopancreas, and muscle after WSSV infection, while HIF-1β remained constitutively expressed. The expression for both LDH subunits increased in each tissue evaluated during the WSSV infection, translating into increased enzyme activity. Glucose concentration increased in each tissue evaluated, while lactate increased in gills and hepatopancreas, but not in muscle. Silencing of HIF-1α blocked the increase of LDH expression and enzyme activity, along with glucose (all tissues) and lactate (gills and hepatopancreas) concentrations produced by WSSV infection. These results demonstrate that HIF-1 up regulates the expression of LDH subunits during WSSV infection, and that this induction contributes to substrate metabolism in energetically active tissues of infected shrimp.

A laminin-receptor-like protein regulates white spot syndrome virus infection by binding to the viral envelope protein VP28 in red claw crayfish Cherax quadricarinatus

White spot syndrome virus (WSSV) is a lethal pathogen of shrimp and many other crustaceans, which has been causing huge economic losses in global aquaculture. Laminin receptor (LR) is a cell surface receptor which participates in the interactions between cells as well as cells and extracellular matrix. Previously, we found that a CqLR-like gene was responsive to WSSV infection in the hematopoietic tissue (Hpt) cells from red claw crayfish Cherax quadricarinatus. To further reveal the role of CqLR-like gene involved in WSSV infection, the full-length cDNA of CqLR-like gene was cloned with 1000 bp, and the open reading frame encoded 308 amino acids with a conserved laminin-binding domain. Importantly, both the WSSV entry and viral replication were strongly reduced in Hpt cells after loss-of-function of CqLR-like gene by gene silencing. Protein interaction assay demonstrated that the recombinant CqLR-like protein could bind to WSSV virion in vitro by enzyme-linked immunosorbent assay and the binding affinity was in a dose-dependent manner. Furthermore, recombinant CqLR-like protein was found to bind to WSSV envelop protein VP28, but not other envelop proteins tested including VP19, VP24, and VP26, by pull down assay in HEK293T cells. In regarding to that LR is mainly localized on many types of cells' membrane, these data together suggested that CqLR-like protein was likely to function as a putative recognition molecule towards WSSV and act in the viral entry into a crustacean host cell, which may benefit the elucidation of the WSSV pathogenesis and further the pharmaceutical target for the possibly effective control of WSSV disease.

WSSV-responsive gene expression under the influence of PmVRP15 suppression

The viral responsive protein 15 from black tiger shrimp Penaeus monodon (PmVRP15), is highly up-regulated and produced in the hemocytes of shrimp with white spot syndrome virus (WSSV) infection. To investigate the differential expression of genes from P. monodon hemocytes that are involved in WSSV infection under the influence of PmVRP15 expression, suppression subtractive hybridization (SSH) of PmVRP15-silenced shrimp infected with WSSV was performed. The 189 cDNA clones of the forward library were generated by subtracting the cDNAs from WSSV-infected and PmVRP15 knockdown shrimp with cDNAs from WSSV-infected and GFP knockdown shrimp. For the opposite subtraction, the 176 cDNA clones in the reverse library was an alternative set of genes in WSSV-infected shrimp hemocytes in the presence of PmVRP15 expression. The abundant genes in forward SSH library had a defense/homeostasis of 26%, energy/metabolism of 23% and in the reverse SSH library a hypothetical protein with unknown function was found (30%). The differential expressed immune-related genes from each library were selected for expression analysis using qRT-PCR. All selected genes from the forward library showed high up-regulation in the WSSV-challenged PmVRP15 knockdown group as expected. Interestingly, PmHHAP, a hemocyte homeostasis associated protein, and granulin-like protein, a conserved growth factor, are extremely up-regulated in the absence of PmVRP15 expression in WSSV-infected shrimp. Only transcript level of transglutaminase II, that functions in regulating hematopoietic tissue differentiation and inhibits mature hemocyte production in shrimp, was obviously down-regulated as observed from SSH results. Taken together, our results suggest that PmVRP15 might have a function relevant to hemocyte homeostasis during WSSV infection.

A VP24-truncated isolate of white spot syndrome virus is inefficient in per os infection

White spot syndrome virus (WSSV) is a major pathogen of penaeid shrimp. Here we identified a new WSSV strain, WSSV-CN04, from naturally infected Marsupenaeus japonicus. Whole genomic sequencing results indicate that the WSSV-CN04 genome was 281 054 bp in length, and encoded 157 hypothetic proteins. The genome sequence of WSSV-CN04 was most closely related to the low-virulent strain WSSV-CN03, sharing 97.5% sequence identity. Notably, in WSSV-CN04, the major envelop protein VP24 was not only truncated but also absent in the virions. Since VP24 was previously reported to be essential for WSSV per os infection by mediating WSSV-chitin interaction, we further analyzed the peroral infection of WSSV-CN03 and -CN04 in Litopenaeus vannamei, and show that the infectivity of WSSV-CN04 was significantly lower than that of WSSV-CN03. When compared with WSSV-CN03-infected shrimp, fewer virions were detected in the digestive tract tissues of WSSV-CN04-infected shrimp at 4 hours post-infection (hpi), and the viral titers in the animals at 24 hpi were much lower. Moreover, a peptide corresponding to VP24 chitin-binding domain reduced the amount of WSSV-CN03 in the midgut to a level similar to that of WSSV-CN04 at 4 hpi. These findings indicate that the truncation of VP24 may attenuate the peroral infectivity of WSSV-CN04, and therefore verify the important role of VP24 in WSSV per os infection.

Delivery of viral recombinant VP28 protein using chitosan tripolyphosphate nanoparticles to protect the whiteleg shrimp, Litopenaeus vannamei from white spot syndrome virus infection

The VP28 gene of white spot syndrome virus was amplified by PCR using gene specific primer set and cloned into pRSET B vector to produce recombinant VP28 (r-VP28) in E. coli GJ1158. The chitosan tripolyphosphate nanoparticles (CS/TPP) were prepared by ionic gelation process and characterized. The purified r-VP28 protein was encapsulated by CS/TPP nanoparticles. The encapsulation efficiency of CS/TPP nanoparticles was found to be 84.8% for r-VP28 protein binding with CS/TPP nanoparticles. The in vitro release profile of encapsulated r-VP28 was determined after treating with protease and chitosanase. The different types of feed were formulated and named as normal feed with PBS, Feed A coated with crude r-VP28, Feed B with purified r-VP28 and Feed C with CS/TPP encapsulated r-VP28 (Purified). Tissue distribution and clearance of r-VP28 at different time intervals were examined in shrimp fed with different types of feed by ELISA and the results showed the presence of r-VP28 protein in different organs. Various immunological parameters were assessed in experimental shrimp. The mRNA expression of five immune-related genes was analysed by qPCR in order to investigate their response to all types of feed in shrimp. A cumulative percentage mortality was also recorded in treated shrimp challenged with WSSV.

The identification of microRNAs involved in the response of Chinese shrimp Fenneropenaeus chinensis to white spot syndrome virus infection

MicroRNA (miRNA) is a class of small noncoding RNA, which is involved in the post-transcriptional regulation in all metazoan eukaryotes. MiRNAs might play an important role in the host response to virus infection. However, miRNAs in the aquatic crustacean species were not extensively investigated. To obtain a better understanding of the response of Chinese shrimp Fenneropenaeus chinensis to white spot syndrome virus (WSSV) infection, the sequence and expression profile of miRNAs in the hepatopancreas of WSSV-infected F. chinensis were obtained by the high-throughput Illumina HiSeq 2500 deep sequencing technique. A total number of 129 known miRNAs and 44 putative novel miRNAs were identified from the deep sequencing data. The peak size of miRNAs was 22 nt (37.0%). 25 miRNAs were significantly (P < 0.05) differentially expressed post WSSV infection. Six of the differentially expressed miRNAs were randomly selected for further verification by the real-time RT-PCR technique. The results showed that there was a consistency between the deep sequencing and real-time RT-PCR assay. The target genes of differentially expressed miRNAs were predicted. Each miRNA had 4 target genes on average. The results suggested that some specific miRNAs might be involved in the response of F. chinensis to WSSV infection, and further provided basic information for the investigation of specific miRNAs in F. chinensis.

Characterization and prevalence of a novel white spot syndrome viral genotype in naturally infected wild crayfish, Procambarus clarkii, in Shanghai, China

White spot syndrome virus (WSSV) infection is commonly detected by vp28-qPCR assay in wild crayfish, Procambarus clarkii, a widespread crustacean species in the aquatic environment in China. The virions of crayfish WSSV have been isolated and purified. Based on TEM observation, they exhibited morphological structures that are identical to known WSSV. In addition, the WSSV major envelope protein VP28 was observed based on Western blot analysis of the total structural proteins of crayfish WSSV. PCR amplification and sequencing analyses of variable regions of ORF14/15, ORF23/24 and ORF94, along with viral genomic sequencing and phylogenomic analysis, indicated that the crayfish WSSV, named WSSV-CN-Pc, represents a new WSSV genotype. Intramuscular injection bioassay revealed that WSSV-CN-Pc was as virulent as the WSSV Taiwan strain. The WSSV-CN-Pc exhibited characteristics of a dominant genotype, with high infection load (107-108 WSSV/mg) and high prevalence (91.7%, 110 of 120 crayfish samples) observed in the surveyed wild crayfish. WSSV-CN-Pc was also detected, with similar infection pattern as observed in crayfish, in farmed Litopenaeus vannamei shrimp that shared similar ecological niches with the sampled crayfish. Our results indicated that there was horizontal transmission of WSSV-CN-Pc between crayfish and shrimp in nature. Our findings also implicated that crayfish and shrimp farming should be integrated and managed with cautions in order to reduce the risk of spread and circulation of WSSV in the aquatic environment.

Resonant Dipolar Coupling of Microwaves with Confined Acoustic Vibrations in a Rod-shaped Virus

In this letter, we treat a rod-shaped virus as a free homogenous nanorod and identify its confined acoustic vibration modes that can cause strong resonant microwave absorption through electric dipolar excitation with a core-shell charge distribution. They are found to be the n = 4N-2 modes of the longitudinal modes of the nanorods, where N is an integer starting from 1 and n is the mode order quantum number. This study was confirmed by measuring the microwave absorption spectra of white spot syndrome virus (WSSV), which is a rod-shaped virus. This is also the first study to identify the “dipolar-like” mode in a rod-shaped nano-object. Our study is not only an important step to achieve rapid and sensitive detection of rod-shaped viruses based on their microwave spectroscopic features and a non-contact method to measure the Young’s modulus of rod-shaped viruses, but also is critical to formulate an efficient epidemic prevention strategy to deactivate viruses with the structure-resonant microwaves.

Contribution of Next-Generation Sequencing to Aquatic and Fish Virology

The recent technological advances in nucleic acid sequencing, called next-generation sequencing (NGS), have revolutionized the field of genomics and have also influenced viral research. Aquatic viruses, and especially those infecting fish, have also greatly benefited from NGS technologies, which provide a huge amount of molecular information at a low cost in a relatively short period of time. Here, we review the use of the current high-throughput sequencing platforms with a special focus on the associated challenges (regarding sample preparation and bioinformatics) in their applications to the field of aquatic virology, especially for: (i) discovering novel viruses that may be associated with fish mortalities, (ii) elucidating the mechanisms of pathogenesis, and finally (iii) studying the molecular epidemiology of these pathogens.

Triosephosphate isomerase (TPI) facilitates the replication of WSSV in Exopalaemon carinicauda

Triosephosphate isomerase (TPI) is a vital enzyme in the glycolytic pathway, which can catalyze the interconversion of glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP). DHAP is involved in lipid metabolism and phospholipid synthesis. In order to know the role of TPI in WSSV infection to prawn, we cloned the full length cDNA of triosephosphate isomerase gene (EcTPI) from Exopalaemon carinicauda, and its function during WSSV infection was analyzed. EcTPI transcripts were widely distributed in all tissues, but showed relatively higher expression levels in the gill and epidermis. Its expression was apparently up-regulated after 24 h post WSSV injection (hpi), when the virus load began to rise. Furthermore, we detected the expressions of the key genes encoding the enzymes which catalyze the key steps in the glycolysis during WSSV infection. The data showed that genes encoding the enzymes which catalyzed upper steps of glycolysis to produce GAP, including hexokinase (HK), glucose-6-phosphate isomerase (GPI) and phosphofructokinase-1 (PFK-1), were significantly up-regulated at 24 and 27 hpi. Genes encoding the enzymes catalyzing down steps of glycolysis after GAP, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH), enolase (ENO) and pyruvate kinase (PK), were apparent down-regulated at 24 and 27 hpi. Meanwhile, the gene encoding the enzyme glycerol-3-phosphate dehydrogenase (GPDH) catalyzing DHAP to glycerol-3-phosphate (G-3-P) showed down-regulation at 12-27 hpi, while the gene encoding dihydroxyacetone-phosphate acyltransferase (DHAPAT) catalyzing DHAP to further synthesis of phospholipids showed up-regulation at 12-24 hpi. These data suggested that WSSV infection could change the glycolysis pathway to make them produce more phospholipids which could be very helpful for virus replication. In order to further confirm the above speculation, dsRNA interference (RNAi) approach was used to knock down EcTPI gene and analyze its effect on WSSV load in prawn. The data showed that interference of EcTPI gene led to a significant decrease of WSSV loads in WSSV infected prawn. These data provided useful information to understand the infection mechanism of WSSV.

WSSV envelope protein VP51B links structural protein complexes and may mediate virus infection

White spot syndrome virus (WSSV), an enveloped double-stranded DNA virus, is the causative agent of a disease that has led to severe mortalities of cultured shrimps in Taiwan and many other countries. In the previous study, Penaeus monodon chitin-binding protein (CBP) and glucose transporter 1 (Glut1), two cell membrane proteins, were found to at least interact with other 10 WSSV envelope proteins including VP51B. These envelope proteins might form a protein complex. According to the known information, VP51B was used to identify its role in the protein complex. Western blotting of the intact viral particles and fractionation of the viral components confirmed that VP51B is one of WSSV envelope proteins. In this study, the protein-protein interaction between VP51B and other WSSV envelope proteins was identified by far-western blot experiment and VP51B was found to interact with VP24, VP31, VP32, VP39B and VP41A. Furthermore, the in vivo neutralization experiment using recombinant VP51B plus with VP39B showed the best inhibition. These data indicate that VP51B participates in the WSSV protein complex and plays an important role in WSSV infection.

cDNA cloning and expression analysis of a phosphopyruvate hydratase gene from the chinese shrimp Fenneropenaeus chinensis

In the present study a cDNA encoding a phosphopyruvate hydratase (enolase) was cloned from the muscle of the Chinese shrimp (Fenneropenaeus chinensis) and named as FcEnolase. The cDNA of FcEnolase encoded a protein of 434 amino acid residues with a molecular mass 47.22 kDa. The residues 342-355 constituted the signature motif "LLLKVNQIGSVTES". A SNP locus (C96T) in the ORF at 96 bp was identified. The results showed that the FcEnolase was a conserved gene. In the normal F. chinensis, the mRNA level in the muscle was much higher (P < 0.05) than the mRNA level in the gill and hepatopancreas. To verify the mRNA level of FcEnolase in the F. chinensis post WSSV infection, a real-time RT-PCR was performed. In the WSSV-infected F. chinensis, the FcEnolase mRNA level was significantly (P < 0.05) up-regulated in the muscle at 12 and 24 h post challenge (hpc) to approximately 2.7-fold and 2.7-fold the mRNA level in the controls, respectively. The FcEnolase mRNA level in the gill was significantly (P < 0.05) down-regulated at 6 hpc to approximately 0.3-fold the mRNA level in the control, followed by a significant (P < 0.05) up-regulation at 12 hpc to approximately 2.8-fold the mRNA level in the control. There was no obvious change of FcEnolase mRNA level in the hepatopancreas during the infection process. The expression profile coincided with the fact that WSSV primarily infects the tissues of muscle and gill, but hardly infects hepatopancreas. To verify the protein level of FcEnolase post WSSV infection, a Western blot was performed. The FcEnolase protein level in the muscle at 24 hpc significantly (P < 0.05) increased to approximately 2.1-fold the level in the control. These results showed the characterization of FcEnolase and suggested that the FcEnolase might be involved in the response of F. chinensis to WSSV infection.

Current Advances on Virus Discovery and Diagnostic Role of Viral Metagenomics in Aquatic Organisms

The global expansion of the aquaculture industry has brought with it a corresponding increase of novel viruses infecting different aquatic organisms. These emerging viral pathogens have proved to be a challenge to the use of traditional cell-cultures and immunoassays for identification of new viruses especially in situations where the novel viruses are unculturable and no antibodies exist for their identification. Viral metagenomics has the potential to identify novel viruses without prior knowledge of their genomic sequence data and may provide a solution for the study of unculturable viruses. This review provides a synopsis on the contribution of viral metagenomics to the discovery of viruses infecting different aquatic organisms as well as its potential role in viral diagnostics. High throughput Next Generation sequencing (NGS) and library construction used in metagenomic projects have simplified the task of generating complete viral genomes unlike the challenge faced in traditional methods that use multiple primers targeted at different segments and VPs to generate the entire genome of a novel virus. In terms of diagnostics, studies carried out this far show that viral metagenomics has the potential to serve as a multifaceted tool able to study and identify etiological agents of single infections, co-infections, tissue tropism, profiling viral infections of different aquatic organisms, epidemiological monitoring of disease prevalence, evolutionary phylogenetic analyses, and the study of genomic diversity in quasispecies viruses. With sequencing technologies and bioinformatics analytical tools becoming cheaper and easier, we anticipate that metagenomics will soon become a routine tool for the discovery, study, and identification of novel pathogens including viruses to enable timely disease control for emerging diseases in aquaculture.

Virulence and genotypes of white spot syndrome virus infecting Pacific white shrimp Litopenaeus vannamei in north-western Mexico

White spot syndrome virus (WSSV) has caused substantial global economic impact on aquaculture, and it has been determined that strains can vary in virulence. In this study, the effect of viral load was evaluated by infecting Litopenaeus vannamei with 10-fold serial dilution of tissue infected with strain WSSV Mx-H, and the virulence of four WSSV strains from north-western Mexico was assessed along with their variable number of tandem repeat (VNTR) genotypes in ORF75, ORF94 and ORF125. The LD₅₀ of the Mx-H strain was a dilution dose of 10^-7.5 ; the mortality titre was 10^9.2 LD₅₀ per gram. In shrimp injected with 10^2.5 to 10^6.5 LD₅₀ , no significant virulence differences were evident. Using mortality data, the four WSSV strains grouped into three virulence levels. The Mx-F strain (intermediate virulence) and the Mx-C strain (high virulence) showed more genetic differences than those observed between the Mx-G (low-virulence) and Mx-H (high-virulence) strains, in ORF94 and ORF125. The application of high-viral-load inocula proved useful in determining the different virulence phenotypes of the WSSV strains from the Eastern Pacific.

Kinetic analysis of internalization of white spot syndrome virus by haemocyte subpopulations of penaeid shrimp, Litopenaeus vannamei (Boone), and the outcome for virus and cell

Little is known about the innate antiviral defence of shrimp haemocytes. In this context, the haemocytes of penaeid shrimp Litopenaeus vannamei (Boone) were separated by iodixanol density gradient centrifugation into five subpopulations (sub): sub 1 (hyalinocytes), sub 2 and 3 (prohyalinocytes), sub 4 (semigranulocytes) and sub 5 (granulocytes) and exposed to beads, white spot syndrome virus (WSSV) and ultraviolet (UV)-killed WSSV. In a first experiment, the uptake of beads, white spot syndrome virus (WSSV) and UV-killed WSSV by these different haemocyte subpopulations was investigated using confocal microscopy. Only haemocytes of sub 1, 4 and 5 were internalizing beads, WSSV and UV-killed WSSV. Beads were engulfed by a much larger percentage of cells (91.2 in sub 1; 84.1 in sub 4 and 58.1 in sub 5) compared to WSSV (9.6 in sub 1; 10.5 in sub 4 and 7.9 in sub 5) and UV-killed WSSV (12.9 in sub 1; 13.3 in sub 4; and 11.8 in sub 5). In a second experiment, it was shown that upon internalization, WSS virions lost their envelope most probably by fusion with the cellular membrane of the endosome (starting between 30 and 60 min post-inoculation) and that afterwards the capsid started to become disintegrated (from 360 min post-inoculation). Expression of new viral proteins was not observed. Incubation of haemocyte subpopulations with WSSV but not with UV-killed WSSV and polystyrene beads resulted in a significant drop in haemocyte viability. To find the underlying mechanism, a third experiment was performed in which haemocyte subpopulations were exposed to a short WSSV DNA fragment (VP19) and CpG ODNs. These small DNA fragments induced cell death. In conclusion, WSSV is efficiently internalized by hyalinocytes, semigranulocytes and granulocytes, after which the virus loses its envelope; as soon as the capsids start to disintegrate, cell death is activated, which in part may be explained by the exposure of viral DNA to cellular-sensing molecules.

Crystal Structure of Major Envelope Protein VP24 from White Spot Syndrome Virus

White spot syndrome virus (WSSV) is one of the major and most serious pathogen in the shrimp industry. As one of the most abundant envelope protein, VP24 acts as a core protein interacting with other structure proteins and plays an important role in virus assembly and infection. Here, we have presented the crystal structure of VP24 from WSSV. In the structure, VP24 consists of a nine-stranded β–barrel fold with mostly antiparallel β-strands, and the loops extending out the β–barrel at both N-terminus and C-terminus, which is distinct to those of the other two major envelope proteins VP28 and VP26. Structural comparison of VP24 with VP26 and VP28 reveals opposite electrostatic surface potential properties of them. These structural differences could provide insight into their differential functional mechanisms and roles for virus assembly and infection. Moreover, the structure reveals a trimeric assembly, suggesting a likely natural conformation of VP24 in viral envelope. Therefore, in addition to confirming the evolutionary relationship among the three abundant envelope proteins of WSSV, our structural studies also facilitate a better understanding of the molecular mechanism underlying special roles of VP24 in WSSV assembly and infection.

Envelope protein VP24 from White spot syndrome virus: expression, purification and crystallization

White spot syndrome virus (WSSV) is a major shrimp pathogen known to infect penaeid shrimp and other crustaceans. VP24 is one of the major envelope proteins of WSSV. In order to facilitate purification, crystallization and structure determination, the predicted N-terminal transmembrane region of approximately 26 amino acids was truncated from VP24 and several mutants were prepared to increase the proportion of selenomethionine (SeMet) residues for subsequent structural determination using the SAD method. Truncated VP24, its mutants and the corresponding SeMet-labelled proteins were purified, and the native and SeMet proteins were crystallized by the hanging-drop vapour-diffusion method. Crystals of VP24 were obtained using a reservoir consisting of 0.1 M Tris-HCl pH 8.5, 2.75 M ammonium acetate with a drop volume ratio of two parts protein solution to one part reservoir solution. Notably, ATP was added as a critical additive to the drop with a final concentration of 10 mM. Crystals of SeMet-labelled VP24 mutant diffracted to 3.0 Å resolution and those of the native diffracted to 2.4 Å resolution; the crystals belonged to space group I213, with unit-cell parameters a = b = c = 140 Å.

Experimental inoculation of Louisiana red swamp crayfish Procambarus clarkii with white spot syndrome virus (WSSV)

The red swamp crayfish Procambarus clarkii represents an important aquaculture species responsible for over half of all commercial aquaculture profits in Louisiana, USA. White spot syndrome virus (WSSV) is highly pathogenic in crustacean species and induces mass mortality in aquaculture operations worldwide. Natural outbreaks of WSSV occur yearly in cultured populations of crayfish in Louisiana. The goal of this study was to better understand the infectivity of WSSV in P. clarkii, by determining the minimum lethal dose necessary to initiate infection and to measure the resulting cumulative mortality following infection with different doses. A real time quantitative PCR (qPCR) method was used to detect WSSV in DNA extracted from gill tissue to ensure P. clarkii study populations were WSSV-free before the start of trials. Viable viral particles were isolated from naturally infected P. clarkii gill tissue and quantified using a novel digital PCR approach. Three infectivity trials were performed, and WSSV inocula were created by serial dilution, generating 5 treatments per trial. Five crayfish (weighing ~25 g) per dilution per trial received viral inoculations. Mortality was monitored daily for the duration of the trial in order to construct a median lethal dose (LD50) curve, and probit regression analysis was used to determine LD50 concentrations of viral particles. Knowledge of the infectivity of WSSV in native crayfish populations is of critical importance to the management of the commercial crayfish aquaculture industry in Louisiana. This is the first study to investigate the infectivity and to determine the LD50 of the Louisiana strain of WSSV in native crayfish.

Cloning of Litopenaeus vannamei CD63 and it's role in white spot syndrome virus infection

White Spot Syndrome Virus (WSSV) is currently the most serious shrimp pathogen, which has brought huge losses to shrimp industry worldwide. CD63 of shrimp belongs to the tetraspanin superfamily, which plays an important role in signal transduction and immune process. In this paper, CD63 cDNA sequence of Litopenaeus vannamei was cloned using RACE method. The amplified sequence is 1472 bp, with its ORF 744 bp, encoding 247 amino acids. Bioinformatics analysis showed that the sequence of LvCD63 has 93% similarity with Penaeus monodon and 92% similarity with Fenneropenaeus chinensis. Real-time PCR analysis showed that the mRNA levels of LvCD63 expressed in the tissues of hemocytes, gill, epithelial tissue, heart, lymphoid, hepatopancreas, stomach, intestines, muscle and nerve. Among these tissues the highest expression level was showed in the tissue of haemolymph, followed by epithelial tissue, hepatopancreas, and nerve. The lowest expression level of LvCD63 was appeared in the muscle tissue. After WSSV challenge, the expression levels of LvCD63 were both up-regulated in the tissues of gill and epithelial. However the expression level of LvCD63 in hepatopancreas was down-regulated. Far-western blot analysis showed that LvCD63 interacts with VP28, and both VP28N and VP28C fragments interact with LvCD63. Flow cytometry analysis showed that LvCD63 was present on the surface of hemocytes and it is required for binding of WSSV virions. Neutral experiments in vivo showed that LvCD63LEL delayed WSSV infection in shrimp.

ICP35 Is a TREX-Like Protein Identified in White Spot Syndrome Virus

ICP35 is a non-structural protein from White spot syndrome virus believed to be important in viral replication. Since ICP35 was found to localize in the host nucleus, it has been speculated that the function of ICP35 might be involved in the interaction of DNA. In this study, we overexpressed, purified and characterized ICP35. The thioredoxin-fused ICP35 (thio-ICP35) was strongly expressed in E. coli and be able to form itself into dimers. Investigation of the interaction between ICP35 and DNA revealed that ICP35 can perform DNase activity. Structural model of ICP35 was successfully built on TREX1, suggesting that ICP35 might adopt the folding similar to that of TREX1 protein. Several residues important for dimerization in TREX1 are also conserved in ICP35. Residue Asn126 and Asp132, which are seen to be in close proximity to metal ions in the ICP35 model, were shown through site-directed mutagenesis to be critical for DNase activity.

Virus-derived small RNAs in the penaeid shrimp Fenneropenaeus chinensis during acute infection of the DNA virus WSSV

Small interfering RNAs (siRNAs) and microRNAs (miRNAs) are two classes of small RNAs (sRNAs) that are critical for virus-host interplay via the RNA interference (RNAi) pathway. One virus-derived siRNA and numerous miRNAs has been reported for the double-stranded DNA virus white spot syndrome virus (WSSV), however, the expression profiles of these different types of sRNAs have not been assessed. Here, by sequencing the sRNAs and mRNAs of WSSV-infected Chinese shrimp (Fenneropenaeus chinensis), we found that the viral transcripts were universally targeted by WSSV-derived siRNAs, supporting a pivotal role for RNAi in the anti-viral immunity of shrimp. The genesis of WSSV-derived siRNAs was associated with long RNA structures. Moreover, by separating miRNAs from siRNAs, 12 WSSV miRNAs were identified. Investigation of conserved viral miRNA targets in different host species indicated the involvement of viral miRNAs in host immune responses. Collectively, our data provide new insights into the role of the RNAi pathway in the interplay between DNA viruses and crustaceans.

The Potential for Microalgae as Bioreactors to Produce Pharmaceuticals

As photosynthetic organisms, microalgae can efficiently convert solar energy into biomass. Microalgae are currently used as an important source of valuable natural biologically active molecules, such as carotenoids, chlorophyll, long-chain polyunsaturated fatty acids, phycobiliproteins, carotenoids and enzymes. Significant advances have been achieved in microalgae biotechnology over the last decade, and the use of microalgae as bioreactors for expressing recombinant proteins is receiving increased interest. Compared with the bioreactor systems that are currently in use, microalgae may be an attractive alternative for the production of pharmaceuticals, recombinant proteins and other valuable products. Products synthesized via the genetic engineering of microalgae include vaccines, antibodies, enzymes, blood-clotting factors, immune regulators, growth factors, hormones, and other valuable products, such as the anticancer agent Taxol. In this paper, we briefly compare the currently used bioreactor systems, summarize the progress in genetic engineering of microalgae, and discuss the potential for microalgae as bioreactors to produce pharmaceuticals.

Genome sequence of Perigonia lusca single nucleopolyhedrovirus: insights into the evolution of a nucleotide metabolism enzyme in the family Baculoviridae

The genome of a novel group II alphabaculovirus, Perigonia lusca single nucleopolyhedrovirus (PeluSNPV), was sequenced and shown to contain 132,831 bp with 145 putative ORFs (open reading frames) of at least 50 amino acids. An interesting feature of this novel genome was the presence of a putative nucleotide metabolism enzyme-encoding gene (pelu112). The pelu112 gene was predicted to encode a fusion of thymidylate kinase (tmk) and dUTP diphosphatase (dut). Phylogenetic analysis indicated that baculoviruses have independently acquired tmk and dut several times during their evolution. Two homologs of the tmk-dut fusion gene were separately introduced into the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) genome, which lacks tmk and dut. The recombinant baculoviruses produced viral DNA, virus progeny, and some viral proteins earlier during in vitro infection and the yields of viral occlusion bodies were increased 2.5-fold when compared to the parental virus. Interestingly, both enzymes appear to retain their active sites, based on separate modeling using previously solved crystal structures. We suggest that the retention of these tmk-dut fusion genes by certain baculoviruses could be related to accelerating virus replication and to protecting the virus genome from deleterious mutation.

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

White spot syndrome virus (WSSV) is a major causative agent in shrimp farming. Consequently, RNAi technology is an effective strategy to prevent WSSV infection in shrimp especially dsRNA targeting to rr2 of WSSV. In an effort to develop dsRNA expression in shrimp for control of WSSV infection, we developed a recombinant baculovirus expressing recombinant VP28 as the gene delivery system to carry a gene encoding dsRNA specific to rr2 for triggering the RNAi process in shrimp. The results showed that the recombinant baculovirus harboring VP28 was able to express VP28 indicated by Western blot with polyclonal antibody specific to VP28. VP28 transcript was detected in shrimp hemocytes after co-culture hemocytes with the recombinant baculovirus displaying VP28. In addition, we found that shrimp injected with the recombinant baculovirus displaying VP28 and encoding dsRNA synthetic gene specific to rr2 (Bac-VP28-dsrr2) showed the lowest cumulative mortality (33%) at 14days post infection (dpi) when compared to shrimp injected with baculovirus displaying VP28 (Bac-VP28) (64% cumulative mortality) (p<0.05). According to the results, shrimp injected with Bac-VP28-dsrr2 also showed significantly lower WSSV copies than shrimp injected with Bac-VP28 (p<0.05) along with the down-regulation of rr2 expression at 1, 3 and 7dpi. In conclusion, the Bac-VP28-dsrr2 was effective in prevention of WSSV infection. Therefore, the results obtained here can be applied to the prevention of WSSV infection by mixing the recombinant baculovirus with shrimp feed in the future.