White Tail Disease Research Articles

Utilisation of probiotics for disease management in giant freshwater prawn (Macrobrachium rosenbergii): Administration methods, antagonistic effects and immune response.

The giant freshwater prawn (Macrobrachium rosenbergii) is a high-yielding prawn variety well-received worldwide due to its ability to adapt to freshwater culture systems. Macrobrachium rosenbergii is an alternative to shrimp typically obtained from marine and brackish aquaculture systems. However, the use of intensive culture systems can lead to disease outbreaks, particularly in larval and post-larval stages, caused by pathogenic agents such as viruses, bacteria, fungi, yeasts and protozoans. White tail disease (viral), white spot syndrome (viral) and bacterial necrosis are examples of economically significant diseases. Given the increasing antibiotic resistance of disease-causing microorganisms, probiotics have emerged as promising alternatives for disease control. Probiotics are live active microbes that are introduced into a target host in an adequate number or dose to promote its health. In the present paper, we first discuss the diseases that occur in M. rosenbergii production, followed by an in-depth discussion on probiotics. We elaborate on the common methods of probiotics administration and explain the beneficial health effects of probiotics as immunity enhancers. Moreover, we discuss the antagonistic effects of probiotics on pathogenic microorganisms. Altogether, this paper provides a comprehensive overview of disease control in M. rosenbergii aquaculture through the use of probiotics, which could enhance the sustainability of prawn culture.

Structural and functional characterization of RNA dependent RNA polymerase of Macrobrachium rosenbergii nodavirus (MnRdRp)

Macrobrachium rosenbergii is a highly valued farmed freshwater species and its production has been affected globally by white tail disease caused by M. rosenbergii nodavirus (MrNV). MrNV is a single stranded positive sense RNA virus encoding RNA-dependent RNA polymerase (RdRp) for genome replication. Due to its essentiality for pathogenesis, it is an important drug target. The domain prediction of the complete sequence revealed the presence of two enzymatic regions namely methyl transferase and RdRp separated by transmembrane region. The predicted three-dimensional (3D) structure of MnRdRp using AlphaFold 2 shows that the structure is composed of three major sub-domains common for other polymerases namely fingers, palm and thumb. Structural similarity search revealed its similarity with other flaviviridea members especially with BVDV RdRp (BvdvRdRp). The structure of fingers and palm sub-domains is more conserved than the thumb sub-domain. A small α-helix named ‘priming helix’ having conserve Tyr was identified at position 829–833 with a potential role in de novo initiation. Analysis of electrostatic potential revealed that nucleotide and template channels are electropositive. Metal binding residues were identified as Asp599, Asp704 and Asp705. The α and β phosphates of incoming nucleotide interact with two Mn2+, Arg455 and Arg537. For recognition of 2′–OH of incoming rNTP, Asp604, Ser661 and Asn670 were identified which can form H-bond network with 2′–OH group. Docking study revealed that Dasabuvir can potentially inhibit MnRdRp. The study concluded that the overall structure and function of MnRdRp are similar to Flaviviridae polymerases and their inhibitors can work against this enzyme. Communicated by Ramaswamy H. Sarma

Meta-analysis of studies on protection provided by different prophylactic agents, their routes of administration and incubation times against nodavirus infection in Macrobrachium rosenbergii

White tail disease caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) is an infection that primarily affects giant freshwater prawns, Macrobrachium rosenbergii, which in turn causes significant economic losses in aquaculture farms worldwide. In response, different prophylactic agents have been studied to improve resistance to this infection. This meta-analysis aims to assess the effectiveness of different prophylactic agents in promoting shrimp survival. Embase, Google Scholar, PubMed, and Scopus search engines were used to search for relevant articles from 2000 to 2022. Articles were screened to only select articles studying crustaceans being given prophylaxis before the disease challenge. Treatments were analyzed on overall survival, and we performed subgroup analysis of treatment type, administration routes, treatment incubation time pre-infection, and whether the prophylactic agents were derived from MrNV, XSV, or a mixture of both. Between the 3 major prophylaxis types, DNA/RNA prophylaxis, viral protein-based prophylaxis, and supplements, all conferred protection against MrNV infection, though no differences between groups were observed. A shorter incubation period (≤ 7 days) conferred better protection, and prophylactic agents from MrNV origin were found to be more effective. A high degree of heterogeneity was detected between studies, necessitating future large-scale studies addressing possible bias.

Diseases of the giant river prawnMacrobrachium rosenbergii: A review for a growing industry

AbstractThe giant river prawn,Macrobrachium rosenbergii, is a major focus of aquaculture in tropical and sub‐tropical regions around the globe. Over the last 30 years, culture ofM.rosenbergiihas increased exponentially as demand has risen both for domestic consumption and for international export trade. As with many aquaculture species increases in production have been accompanied by the emergence of diseases affecting yield, profit and trading potential. Disease‐causing agents include pathogens infecting other crustaceans, such asDecapod Iridescent Virus(DIV1), as well as pathogens only known fromM.rosenbergiisuch as White Tail Disease caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV). Here, we review the pathogenic agents associated with the culture ofM.rosenbergiisince commercial culture began in earnest during the 1970s. Particular emphasis is given to pathogens first identified in other aquaculture host species, but which have subsequently been shown to infect and cause disease inM.rosenbergii. As polyculture ofM.rosenbergiiwith other aquaculture species is common practice, including culture with other decapods, crabs and fish, increased pathogen transfer among these farmed species may occur asM.rosenbergiiaquaculture increases in the future.

Detection of Macrobrachium rosenbergii Nodavirus (MrNV) of White Tail Disease (WTD) in Apparently Healthy Giant Freshwater Prawn, Macrobrachium rosenbergii in Korea

White tail disease (WTD) is caused by the Macrobrachium rosenbergii nodavirus (MrNV) and an extra-small virus (XSV). MrNV belongs to the Nodaviridae family. While the role of XSV in the pathogenicity of WTD remains unclear, MrNV is considered to be a significant factor in the disease. To study WTD infection in giant freshwater prawns (Macrobrachium rosenbergii), adult and post-larval (PL) prawns were collected from three giant freshwater prawn farms in Gyeongsangnam-do, Korea in 2021. Although the adult and PL prawns did not display any gross signs of WTD, MrNV was detected in both adult and PL in this study. However, XSV was not detected in both prawns. Phylogenetic analysis revealed that the capsid protein gene sequences of MrNV obtained in this study were robustly clustered with the MrNV group, and were clearly distinguished from Alphanodavirus and Betanodavirus groups of the family Nodaviridae. Although Zenker’s necrosis and myolysis were observed histopathologically in the abdominal striated muscle of adult and PL prawns, no gross signs associated with white tail were observed because of local lesions.

Genetic Reassortment between Endemic and Introduced Macrobrachium rosenbergii Nodaviruses in the Murray-Darling Basin, Australia.

Macrobrachium rosenbergii nodavirus (MrNV)—the aetiological agent of white tail disease—is a major limiting factor of crustacean aquaculture as it causes up to 100% mortality in M. rosenbergii larvae and juveniles. Despite the importance of MrNV, there have been few studies on the phylogenetic diversity and geographic range of this virus in Australian waterways. Here, we detected MrNV genomes in common carp (Cyprinus carpio) metatranscriptomes sampled at five freshwater sites across the Murray-Darling Basin (MDB), Australia. We identified genetic divergence of the RNA-dependent RNA polymerase gene between MrNV sequences identified in the northern and southern rivers of the MDB. Northern viruses exhibited strong phylogenetic clustering with MrNV from China, whereas the southern viruses were more closely related to MrNV from Australia. However, all five viruses were closely related in the capsid protein, indicative of genetic reassortment of the RNA1 and RNA2 segments between Australian and introduced MrNV. In addition, we identified Macrobrachium australiense in two of the five MrNV-positive libraries, suggesting that these species may be important reservoir hosts in the MDB. Overall, this study reports the first occurrence of MrNV outside of the Queensland region in Australia and provides evidence for genetic reassortment between endemic and introduced MrNV.

Virus-like particles of Macrobrachium rosenbergii nodavirus: Particle size and capsid protein assembly domain

Macrobrachium rosenbergii nodavirus (MrNv) causes white tail disease (WTD) in the giant freshwater prawn, which poses a major issue in the aquaculture sector. The capsid protein (CP) of MrNv expressed in Escherichia coli self-assembles into virus-like particles (VLPs) with a triangulation number, T = 3. However, the region in MrNv CP that involved in the viral capsid formation has yet to be identified. In the present study, a series of N- and C-terminal MrNv CP deletion mutants were constructed based on the viral subatomic structure. These mutants were then expressed in E. coli and purified with an immobilized metal affinity chromatography (IMAC). The formation of VLPs was determined using transmission electron microscopy (TEM). The results showed that, the first 29 amino acid residues at the N-terminal end of CP are dispensable for VLP formation, but deletion of these residues produced a smaller VLP. Disruption of the CP N-terminal arm (NTA) that contains a β-annulus motif resulted in no protein expression in E. coli. The β-annulus peptide was chemically synthesized, and analysed with TEM, dynamic light scattering (DLS), size-exclusion chromatography (SEC) and native agarose gel electrophoresis, but it did not assemble into VLPs. Truncation of the entire protruding (P) domain did not disrupt the VLP formation. However, deletion of the amino acid residues involved in dimeric interaction between subunits in the shell (S) domain impaired VLP assembly. In conclusion, the minimum contiguous sequence of the CP required for VLP formation was delineated in residues 30 and 252. This study provides mechanistic insights into the assembly of MrNv VLP, which will further broaden its applications in vaccine development and nucleic acid delivery.

White tail disease

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Regulation of Proteolytic Activity to Improve the Recovery of Macrobrachium rosenbergii Nodavirus Capsid Protein.

The causative agent of white tail disease (WTD) in the giant freshwater prawn is Macrobrachium rosenbergii nodavirus (MrNV). The recombinant capsid protein (CP) of MrNV was previously expressed in Escherichia coli, and it self-assembled into icosahedral virus-like particles (VLPs) with a diameter of approximately 30 nm. Extensive studies on the MrNV CP VLPs have attracted widespread attention in their potential applications as biological nano-containers for targeted drug delivery and antigen display scaffolds for vaccine developments. Despite their advantageous features, the recombinant MrNV CP VLPs produced in E. coli are seriously affected by protease degradations, which significantly affect the yield and stability of the VLPs. Therefore, the aim of this study is to enhance the stability of MrNV CP by modulating the protease degradation activity. Edman degradation amino acid sequencing revealed that the proteolytic cleavage occurred at arginine 26 of the MrNV CP. The potential proteases responsible for the degradation were predicted in silico using the Peptidecutter, Expasy. To circumvent proteolysis, specific protease inhibitors (PMSF, AEBSF and E-64) were tested to reduce the degradation rates. Modulation of proteolytic activity demonstrated that a cysteine protease was responsible for the MrNV CP degradation. The addition of E-64, a cysteine protease inhibitor, remarkably improved the yield of MrNV CP by 2.3-fold compared to the control. This innovative approach generates an economical method to improve the scalability of MrNV CP VLPs using individual protease inhibitors, enabling the protein to retain their structural integrity and stability for prominent downstream applications including drug delivery and vaccine development.

The Macrobrachium rosenbergii nodavirus: a detailed review of structure, infectivity, host immunity, diagnosis and prevention

AbstractThe Macrobrachium rosenbergii nodavirus causes white tail disease, which primarily infects giant freshwater prawns, Macrobrachium rosenbergii. The infection leads to almost 100% mortality in post‐larvae, causing significant economic losses in aquaculture farms. To develop effective measures against outbreaks, a good understanding of the virus is essential. In this review, we discuss key aspects of the Macrobrachium rosenbergii nodavirus including its structure, mechanisms of transmission and infection and common strategies for detection and prevention of outbreaks. Structurally, cryogenic electron microscopy revealed that the nodavirus has a T = 3 icosahedral structure with dimeric blade‐like spikes on its surface. Homology modelling comparing wild‐type and enzymatically cleaved Macrobrachium rosenbergii nodavirus‐like particles revealed the significance of these spikes or protruding domains for binding. In vitro and in vivo studies have identified key aspects of Macrobrachium rosenbergii nodavirus infectivity, including (i) the viral binding targets such as transglutaminase and caveolin‐1, (ii) utilisation of B2‐like proteins in promoting infectivity and intracellular migration, (iii) replication mechanisms and (iv) co‐infection with the extra small virus. Though susceptible at a post‐larvae stage, adult Macrobrachium rosenbergii is immune to Macrobrachium rosenbergii nodavirus infection. During outbreaks, polymerase chain reaction and in situ hybridisation‐based detection techniques are commonly used to identify infected populations. Currently, the most useful strategies for an outbreak are physical biosecurity measures and prophylaxis such as vaccination and immunostimulants. Finally, critical gaps in research include development of immortalised shrimp cell models, elucidation of time‐resolved protein changes post‐infection and development of therapies to treat infections to mitigate economic losses during outbreaks.

On-site detection of nodavirus in post larval (PL) stage of the giant prawn, Macrobrachium rosenbergii: A test to nip the problem in the bud

Macrobrachium rosenbergii nodavirus (MrNV) affects the larval, post-larval, and juvenile stages of M. rosenbergii, the giant freshwater prawn, causing white tail disease (WTD). With its high mortality, WTD is a severe threat to shrimp and prawn farming. We describe the development and optimization of an antibody-based lateral flow assay (LFA) for the early detection of MrNV in the post-larval (PL) stage of M. rosenbergii. The LFA parameters (viz., the detergent concentration, GNPs-antibody conjugate, antibody concentration applied to the test line and membrane porosity) were optimized using the design of experiment (L9 orthogonal array). Under optimized conditions, MrNV could be detected within 20 min with high specificity, reproducibility, and sensitivity (LOD = 104 particles/ng of total RNA). In virus challenge experiments, MrNV could be detected on the seventh day of infection in the PL stage. LFA was validated using infected PL samples collected from the field (hatcheries and nurseries) (n = 80) in conjunction with ‘gold standard’ qRT-PCR test. High sensitivity (100%) and specificity (90%) of LFA, with a Cohen's kappa coefficient of 0.936, suggested ‘good agreement’ between the developed LFA and qRT-PCR. The developed LFA has an immense potential of averting losses by rapid detection of MrNV at PL stage in M. rosenbergii.

Genomic and antibody-based assays for the detection of Indian strains of Macrobrachium rosenbergii nodavirus and extra small virus associated with white tail disease of Macrobrachium rosenbergii.

White tail disease (WTD) of cultured Macrobrachium rosenbergiiis caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV). Since both the viruses have small single strand RNA as genetic material with short generation time, they are more prone to mutations. Hence detection methods developed for one strain may be suboptimal for the detection of isolates from the different geographical locations. In the present study two new genomic based methods (RT-PCR and dot-blot hybridization) along with one immunological method (polyclonal antibodies based detection) were developed for the detection of Indian isolates of MrNV and XSV. Among genomic based methods, RT-PCR assay developed was most sensitive. Sensitivity of detection of RT-PCR was 1fg (both MrNV and XSV) of total RNA extracted from purified viral inoculum preparation. In case of WTD positive whole tissue total RNA, the limit of detection was 10fg for both MrNV and XSV. Dot-blot hybridization had a detection limit of 10pg and 0.1ng for MrNV and XSV respectively when RNA extracted from viral inoculum preparation was used; 0.1ng and 1ng when WTD positive whole tissue total RNA was used. Polyclonal antibodies against recombinant proteins (MrNV and XSV capsid) were synthesised. Western blotting and indirect ELISA revealed that the antibodies produced to be specific and highly sensitive. Recombinant protein (antigen) of MrNV and XSV capsid were detected at the dilution of 1:8000. However in case of infected prawn tissue sample, MrNV and XSV were detected at the dilution of 1:32,000 and 1:64,000 respectively. All methods developed are field applicable.

Recombinant viral proteins delivered orally through inactivated bacterial cells induce protection in Macrobrachium rosenbergii (de Man) against White Tail Disease.

White tail disease (WTD) is a disease of Macrobrachium rosenbergii caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) with the potential to devastate the aquaculture industry. The present study aimed to explore the possible protection of M. rosenbergii against the disease by oral administration of bacterially expressed recombinant capsid proteins of MrNV and XSV. Juvenile M.rosenbergii were fed with the feed coated with inactivated bacteria encapsulated expressed recombinant viral proteins either individually or in combination for 7days. Challenge studies using WTD causing agents were carried out after 3 (group I), 10 (group II) and 20 (group III) days post-feeding of viral proteins. Recombinant capsid protein of MrNV showed better protection when compared to other treatments with relative per cent survival of 62.5% (group I), 57.9% (group II) and 39.5% (group III). Treatment controls of groups I, II and III showed 100%, 95% and 95% mortality, respectively. The study demonstrates that oral administration of recombinant capsid proteins of MrNV and XSV provides effective protection against WTD in freshwater prawn.

Macrobrachium rosenbergii nodavirus virus-like particles attach to fucosylated glycans in the gills of the giant freshwater prawn.

The Macrobrachium rosenbergii nodavirus (MrNV), the causative agent of white-tail disease (WTD) in many species of shrimp and prawn, has been shown to infect hemocytes and tissues such as the gills and muscles. However, little is known about the host surface molecules to which MrNV attach to initiate infection. Therefore, the present study investigated the role of glycans as binding molecules for virus attachment in susceptible tissues such as the gills. We established that MrNV in their virus-like particle (MrNV-VLP) form exhibited strong binding to gill tissues and lysates, which was highly reduced by the glycan-reducing periodate and PNGase F. The broad, fucose-binding Aleuria Aurantia lectin (AAL) highly reduced MrNV-VLPs binding to gill tissue sections and lysates, and efficiently disrupted the specific interactions between the VLPs and gill glycoproteins. Furthermore, mass spectroscopy revealed the existence of unique fucosylated LacdiNAc-extended N-linked and O-linked glycans in the gill tissues, whereas beta-elimination experiments showed that MrNV-VLPs demonstrated a binding preference for N-glycans. Therefore, the results from this study highly suggested that MrNV-VLPs preferentially attach to fucosylated N-glycans in the susceptible gill tissues, and these findings could lead to the development of strategies that target virus-host surface glycan interactions to reduce MrNV infections.

Major viral diseases in culturable penaeid shrimps: a review

The practice and development of the culture of commercially important penaeid shrimp results in the occurrence of infectious and non-infectious diseases worldwide. Most of the diseases are caused by the opportunistic microorganisms which are part of the microflora and fauna of the penaeid shrimp. Once the pathogens get a favourable condition, it will cause diseases to the host organisms. Most of the organisms are ubiquitous and are found and reported all over the cultured area in the world. The pathogens are the bacteria, viruses, parasites and protozoans. Viruses are the most important disease-causing agents in penaeid shrimps. The penaeid viruses are widely spread in geographical areas of shrimp culture. The shipment of broodstock and post larvae from one geographical region to another region often results in spreading of viral diseases. The penaeid viruses are the Whispovirus, white spot syndrome virus (WSSV), Penaeus monodon baculovirus (monodon baculovirus), infectious hypodermal and haematopoietic necrosis virus (IHHNV), infectious myonecrosis virus (IMNV), Taura syndrome virus (TSV), yellow head virus (YHV), white tail disease (WTD), covert mortality nodavirus (CMNV), Laem–Singh virus (LSNV) and shrimp haemocyte iridescent virus (SHIV). The review examines and highlights the aquaculture penaeid shrimp viral diseases in detail and concludes the need and importance of severe disease surveillance of the global countries through networking and coordination to safeguard the aquaculture practice for our future generation.

Codon deoptimization of the viral capsid protein-encoding gene attenuates Macrobrachium rosenbergii nodavirus

The aquaculture production of giant freshwater prawn, Macrobrachium rosenbergii has been hampered by the outbreak of white tail disease, which is caused by Macrobrachium rosenbergii nodavirus (MrNV) infection, a virus from the family of Nodaviridae. It is a non-enveloped icosahedral RNA virus, which contains two segments of single-stranded positive-sense RNA genome; namely RNA1 and RNA2. To-date, there is no effective prophylactic or therapeutic agent available to control its outbreak. Current study aimed to attenuate MrNV through the manipulation of synonymous codon usage bias, in order to deoptimize the codon of the viral RNA2 segment, which encodes the viral capsid protein. A total number of 125 synonymous codon substitutions were introduced into the viral RNA2. Resulted in the designed mutant RNA2 to possess 84% nucleotide sequence similarity compared to the wild-type. Viral genes (wild type RNA1, RNA2, and mutant RNA2) that were harboured by respective pUC57 plasmid, were subsequently expressed through in-vitro transcription using T7 promoter and then, transfected into confluent Sf9 cells. The pathogenicity of these clones were compared between non-infected control cells, cells transfected with the wild-type and the attenuated clone, respectively. The comparison of pathogenicity was based on phenotypic examination of the transfected Sf9 cells. Sf9 cells transfected with the wild-type clone exhibited cytopathogenic effects, which include increased in size due to cytoplasmic swelling, and aggregation of the infected cells into clumps of various sizes. While Sf9 cells transfected with the mutant clone exhibited insignificant cytoplasmic swelling and cellular aggregations. The presence of viral genes in the transfected Sf9 cells at 92 h post transfection confirmed the infectivity of both wild-type and mutant clones. Results indicated that the mutant clone was attenuated.

Modified MrNV viral capsids with GE11 peptide for binding colorectal cancer cells.

Virus‐like particles (VLPs) are useful nanoparticles with a great impact on medical nanotechnology. Macrobrachium rosenbergii nodavirus (MrNV), which causes white tail disease (WTD) in giant freshwater prawns, is an icosahedral virus and have 26–27 nm. Recombinant MrNV capsid proteins in Escherichia coli exhibit the self‐assembly of the attractive property of the nanocontainers. Therefore, we hypothesized that modified VLPs either by genetic modification on the C‐terminal domain should enhance specific targeting of VLPs to the destiny of cancer cells. This work thus aims to predict and test the exterior surface of MrNV capsids by genetic modification by the structural modeling and In vitro analysis. We engineered the GE11 peptide to replace the 349–360 residues of the MrNV protruding domain, to insert between the 354 and 355 residues of the MrNV protruding domain and to extend to the C‐terminal of the MrNV capsids, which presumably led the specific binding of modified VLPs to EGFR on cancer cells. However, the site for introducing GE11 peptide into protein still difficult to determine. Therefore, we use the computational method to submit algorithms Phyre2 and Swiss model for the structural prediction. All of the models modified MrNV‐VLPs with GE11 are purified and analyzed by SDS‐PAGE, western blot and TEM analysis. These results lead to an In vitro experiment to enhance binding into EGFR positive cancer cells. This research thus provides a fundamental insight of virus capsid structure and ultimately leads to the development of strategies in drug delivery for carrying therapeutic agents towards the specific host cells.

In experimental challenge with infectious clones of Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV), MrNV alone can cause mortality in freshwater prawn (Macrobrachium rosenbergii)

To overcome the lack of immortal shrimp cell lines for shrimp viral research, we constructed and tested DNA infectious clones of Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) often found together in freshwater prawn (M. rosenbergii) exhibiting white tail disease (WTD). Full-length cDNAs of MrNV and XSV genomic RNA were individually inserted into the baculovirus pFastBacDUAL shuttle vector. Individual Sf9 (insect cell line) transfection resulted in production of RNA (RT-PCR) and capsid proteins (immunofluorescence) for both viruses. Presence of respective virions was confirmed by density gradient purification followed by RT-PCR and transmission electron microscopy. Infectivity was by tested in immersion-challenge tests with M. rosenbergii post-larvae (PL) using both semi-purified viruses, individually or combined, and confirmed by histological analysis (morphology and immunofluorescence) and quantitative RT-PCR. Mortality accompanied by WTD lesions occurred with MrNV alone or in combination with XSV but not with XSV alone, despite its replication.

Transcriptomic analysis of Macrobrachium rosenbergii (giant fresh water prawn) post-larvae in response to M. rosenbergii nodavirus (MrNV) infection: de novo assembly and functional annotation

BackgroundMacrobrachium rosenbergii, is one of a major freshwater prawn species cultured in Southeast Asia. White tail disease (WTD), caused by Macrobrachium rosenbergii nodavirus (MrNV), is a serious problem in farm cultivation and is responsible for up to 100% mortality in the post larvae stage. Molecular data on how M. rosenbergii post-larvae launches an immune response to an infection with MrNV is not currently available. We therefore compared the whole transcriptomic sequence of M. rosenbergii post-larvae before and after MrNV infection.ResultsTranscriptome for M. rosenbergii post-larvae demonstrated high completeness (BUSCO Complete: 83.4%, fragmentation: 13%, missing:3.3%, duplication:16.2%; highest ExN50 value: 94%). The assembled transcriptome consists of 96,362 unigenes with N50 of 1308 bp. The assembled transcriptome was successfully annotated against the NCBI non-redundant arthropod database (33.75%), UniProt database (26.73%), Gene Ontology (GO) (18.98%), Evolutionary Genealogy of Genes: Non-supervised Orthologous Groups (EggNOG) (20.88%), and Kyoto Encyclopedia of Genes and Genome pathway (KEGG) (20.46%). GO annotations included immune system process, signaling, response to stimulus, and antioxidant activity. Differential abundance analysis using EdgeR showed 2413 significantly up-regulated genes and 3125 significantly down-regulated genes during the infection of MrNV.ConclusionsThis study reported a highly complete transcriptome from the post-larvae stage of giant river prawn, M. rosenbergii. Differential abundant transcripts during MrNV infection were identified and validated by qPCR, many of these differentially abundant transcripts as key players in antiviral immunity. These include known members of the innate immune response with the largest expression change occurring in the M. rosenbergii post-larvae after MrNV infection such as antiviral protein, C-type lectin, prophenol oxidase, caspase, ADP ribosylation factors, and dicer.

The atomic structures of shrimp nodaviruses reveal new dimeric spike structures and particle polymorphism

Shrimp nodaviruses, including Penaeus vannamei (PvNV) and Macrobrachium rosenbergii nodaviruses (MrNV), cause white-tail disease in shrimps, with high mortality. The viral capsid structure determines viral assembly and host specificity during infections. Here, we show cryo-EM structures of T = 3 and T = 1 PvNV-like particles (PvNV-LPs), crystal structures of the protrusion-domains (P-domains) of PvNV and MrNV, and the crystal structure of the ∆N-ARM-PvNV shell-domain (S-domain) in T = 1 subviral particles. The capsid protein of PvNV reveals five domains: the P-domain with a new jelly-roll structure forming cuboid-like spikes; the jelly-roll S-domain with two calcium ions; the linker between the S- and P-domains exhibiting new cross and parallel conformations; the N-arm interacting with nucleotides organized along icosahedral two-fold axes; and a disordered region comprising the basic N-terminal arginine-rich motif (N-ARM) interacting with RNA. The N-ARM controls T = 3 and T = 1 assemblies. Increasing the N/C-termini flexibility leads to particle polymorphism. Linker flexibility may influence the dimeric-spike arrangement.