Electron microscopic observation on a non-occluded baculo-like virus in shrimps

Multiple Nucleocapsid Structural Forms of Shrimp White Spot Syndrome Virus Suggests a Novel Viral Morphogenetic Pathway

White spot syndrome virus (WSSV) is a very large dsDNA virus. The accepted shape of the WSSV virion has been as ellipsoidal, with a tail-like extension. However, due to the scarcity of reliable references, the pathogenesis and morphogenesis of WSSV are not well understood. Here, we used transmission electron microscopy (TEM) and cryogenic electron microscopy (Cryo-EM) to address some knowledge gaps. We concluded that mature WSSV virions with a stout oval-like shape do not have tail-like extensions. Furthermore, there were two distinct ends in WSSV nucleocapsids: a portal cap and a closed base. A C14 symmetric structure of the WSSV nucleocapsid was also proposed, according to our Cryo-EM map. Immunoelectron microscopy (IEM) revealed that VP664 proteins, the main components of the 14 assembly units, form a ring-like architecture. Moreover, WSSV nucleocapsids were also observed to undergo unique helical dissociation. Based on these new results, we propose a novel morphogenetic pathway of WSSV.

Metabolic responses of whiteleg shrimp to white spot syndrome virus (WSSV)

Outbreaks of white spot syndrome virus (WSSV) have caused serious damage to penaeid shrimp aquaculture worldwide. Despite great efforts to characterize the virus, the conditions that lead to infection and the infection mechanisms, there is still a lack of understanding regarding these complex virus-host interactions, which is needed to develop consistent and effective treatment methods for WSSV. In this study, we used a gas chromatography - mass spectrometry (GC-MS)-based metabolomics approach to compare the metabolite profiles of gills, haemolymph and hepatopancreas from whiteleg shrimp (Penaeus vannamei) exposed to WSSV and corresponding controls. The results revealed clear discriminations between metabolite profiles of WSSV-challenged shrimp and controlled shrimp in each tissue. The responses of shrimp gills to WSSV infection were characterized by increases of many fatty acids and amino acids in WSSV-challenged shrimp compared to the controls. Changes in haemolymph metabolite profiles include the increased levels of itaconic acid, energy-related metabolites, metabolites in glutathione cycle and decrease of amino acids. The WSSV challenge led to the decreases of several fatty acids and amino acids and increases of other amino acids, lactic acid and other organic compounds (levulinic acid, malonic acid and putrescine) in hepatopancreas. These alterations of shrimp metabolites suggest several immune responses of shrimp to WSSV in a tissue-specific manner, including upregulation of osmoregulation, antimicrobial activity, metabolic rate, gluconeogenesis, glutathione pathway in control of oxidative stress and shift from aerobic to anaerobic metabolism in shrimp which indicates the Warburg effect. The findings from this study provide a better understanding of molecular process of shrimp response against WSSV invasion which may be useful for development of disease management strategies.

A new insight to biomarkers related to resistance in survived-white spot syndrome virus challenged giant tiger shrimp, Penaeus monodon

The emergence of diseases such as white spot disease has become a threat to Penaeus monodon cultivation. Although there have been a few studies utilizing RNA-Seq, the cellular processes of host-virus interaction in this species remain mostly anonymous. In the present study, P. monodon was challenged with WSSV by intramuscular injection and survived for 12 days. The effect of the host gene expression by WSSV infection in the haemocytes, hepatopancreas and muscle of P. monodon was studied using Illumina HiSeq 2000. The RNA-Seq of cDNA libraries was developed from surviving WSSV-challenged shrimp as well as from normal healthy shrimp as control. A comparison of the transcriptome data of the two groups showed 2,644 host genes to be significantly up-regulated and 2,194 genes significantly down-regulated as a result of the infection with WSSV. Among the differentially expressed genes, our study discovered HMGB, TNFSF and c-Jun in P. monodon as new potential candidate genes for further investigation for the development of potential disease resistance markers. Our study also provided significant data on the differential expression of genes in the survived WSSV infected P. monodon that will help to improve understanding of host-virus interactions in this species.

Caspase-3C gene from red swamp crayfish, Procambarus clarki: Characterization and expression in response to pathogenic infection

The caspase is an essential module in the Drosophila immune deficiency (IMD) pathway, which plays a crucial role in countering pathogen infection. In this study, a gene named PcCaspase-3C was found in Procambarus clarkia with a full-length of 4684 bp, including a 1572 bp opening reading frame, which encoded a putative protein of 523 amino acids. PcCaspase-3C contained a CASc domain constituted of 237 amino acids. The PcCaspase-3C gene was primarily expressed in heart, stomach, and intestine, while less in gonad, hepatopancreas, gills, and hemocytes, with the least expression in muscle. Infection with Staphyloccocus aureus, Vibrio parahaemolyticus or white spot syndrome virus (WSSV) induced an up-regulated expression of PcCaspase-3C in intestine or stomach to varying degrees. When PcCaspase-3C was silenced by double-stranded RNA, the expression of some antimicrobial peptides such as ALF2, ALF5, ALF6, Cru3, Cru4, and Lys was significantly inhibited. In addition, silencing of PcCaspase-3C accelerated infection with WSSV in vivo. According to these results, we suggest that PcCaspase-3C might play a crucial role in the immune response of P. clarkia against pathogenic bacterial and viral infections.

A study of the role of glucose transporter 1 (Glut1) in white spot syndrome virus (WSSV) infection

White spot syndrome virus (WSSV) is a large enveloped DNA virus, and it causes a serious disease that has led to severe mortalities of cultured shrimps in many countries. To determine the mechanism of virus entry into the cell and to establish an antiviral strategy, the cell receptor for virus entry and receptor binding protein should be identified. A shrimp cell surface protein, glucose transporter1 (Glut1), was found to interact with WSSV in previous study. In this study, this Glut1 was confirmed to have the ability of transporting glucose, and this gene can also be found in other shrimp species. The interaction between Glut1 and some other WSSV envelope proteins in the infectome structure was verified by far western blot and His pull down assay. In vitro and in vivo neutralization using recombinant partial Glut1 revealed that the large extracellular portion of Glut1 could delay WSSV infection. Also, shrimps which were knocked-down Glut1 gene by treated with dsRNA before WSSV challenge showed decreased mortality. These results indeed provide a direction to develop efficient antiviral strategies or therapeutic methods by using Glut1.

Cloning and characterization of cytoplasmic dynein intermediate chain in Fenneropenaeus chinensis and its essential role in white spot syndrome virus infection

To investigate the role of cytoplasmic dynein in white spot syndrome virus (WSSV) infection, the full-length cDNA of cytoplasmic dynein intermediate chain (FcDYNCI) was cloned in Fenneropenaeus chinensis, which consists of 2582 bp and encodes a polypeptide of 660 amino acids. Sequence analysis and multiple sequence alignment displayed that FcDYNCI was a member of cytoplasmic dynein 1 family. The FcDYNCI mRNA was most highly expressed in hemocytes, which was significantly up-regulated post WSSV infection. At 12 h post infection (hpi), confocal microscopic observation showed that WSSV could be co-localized with cytoplasmic dynein in hemocytes. After silencing by specific FcDYNCI dsRNA, the FcDYNCI mRNA level and the protein amount of FcDYNCI in hemocytes both exhibited a significant reduction, and the expression levels of three WSSV genes ie1, wsv477 and vp28 all exhibited the greatest decreases at 24 hpi. These results suggested that cytoplasmic dynein was involved in WSSV infection.

Molecular immune response of the American lobster (Homarus americanus) to the White Spot Syndrome Virus

The adult American lobster (Homarus americanus) is susceptible to few naturally occurring pathogens, and no viral pathogen is known to exist. Despite this, relatively little is known about the H. americanus immune system and nothing is known about its potential viral immune response. Hundreds of rural communities in Atlantic Canada rely on the lobster fishery for their economic sustainability and could be devastated by large-scale pathogen-mediated mortality events. The White Spot Syndrome Virus is the most economically devastating viral pathogen to global shrimp aquaculture production and has been proposed to be capable of infecting all decapod crustaceans including the European Lobster. An in vivo WSSV injection challenge was conducted in H. americanus and WSSV was found to be capable of infecting and replicating within lobsters held at 20°C. The in vivo WSSV challenge also generated the first viral disease model of H. americanus and allowed for the high-throughput examination of transcriptomic changes that occur during viral infection. Microarray analysis found 136 differentially expressed genes and the expression of a subset of these genes was verified using RT-qPCR. Anti-lipopolysaccharide isoforms and acute phase serum amyloid protein A expression did not change during WSSV infection, contrary to previous findings during bacterial and parasitic infection of H. americanus. This, along with the differential gene expression of thioredoxin and trypsin isoforms, provides compelling evidence that H. americanus is capable of mounting an immune response specific to infection by different pathogen classes.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.

Knocking down caspase-3 by RNAi reduces mortality in Pacific white shrimp Penaeus (Litopenaeus) vannamei challenged with a low dose of white-spot syndrome virus

Apoptosis has long been observed in viral target organs of white-spot syndrome virus (WSSV)-infected shrimp and whether the phenomenon helps the shrimp to survive the infection or is a factor leading to mortality is still controversial. If the shrimp mortality is a result of triggered apoptosis, then inactivation of caspase-3, a key protein in the induction of apoptosis, should improve shrimp survival upon challenge with WSSV. To test this prediction, we identified and characterized a caspase-3 homologue (cap-3) from the Pacific white shrimp Penaeus (Litopenaeus) vannamei and used this information to silence cap-3 expression by RNA interference prior to WSSV challenge. After confirming the efficacy of cap-3 silencing, its effects on mortality at high and low doses of WSSV were evaluated. In a high-dose WSSV challenge, cap-3 silencing had no significant effect on WSSV-induced mortality, except for a delay in mean time to death. However, at a low-dose WSSV challenge, cap-3 silencing correlated with a lower level of cumulative mortality, relative to silencing of a control gene, suggesting that apoptosis may exacerbate rather than decrease mortality in WSSV-challenged shrimp.

Expression, purification and crystallization of two major envelope proteins from white spot syndrome virus

White spot syndrome virus (WSSV) is a major virulent pathogen known to infect penaeid shrimp and other crustaceans. VP26 and VP28, two major envelope proteins from WSSV, have been identified and overexpressed in Escherichia coli. In order to facilitate purification and crystallization, predicted N-terminal transmembrane regions of approximately 35 amino acids have been truncated from both VP26 and VP28. Truncated VP26 and VP28 and their corresponding SeMet-labelled proteins were purified and the SeMet proteins were crystallized by the hanging-drop vapour-diffusion method. Crystals of SeMet-labelled VP26 were obtained using a reservoir consisting of 0.1 M citric acid pH 3.5, 3.0 M sodium chloride and 1%(w/v) polyethylene glycol 3350, whereas SeMet VP28 was crystallized using a reservoir solution consisting of 25% polyethylene glycol 8000, 0.2 M calcium acetate, 0.1 M Na HEPES pH 7.5 and 1.5%(w/v) 1,2,3-heptanetriol. Crystals of SeMet-labelled VP26 diffract to 2.2 A resolution and belong to space group R32, with unit-cell parameters a = b = 73.92, c = 199.31 A. SeMet-labelled VP28 crystallizes in space group P2(1)2(1)2(1), with unit-cell parameters a = 105.33, b = 106.71, c = 200.37 A, and diffracts to 2.0 A resolution.

A review of potential pathogens of sea lice and the application of cleaner fish in biological control

There are many examples of successful biological control of pest populations in aquatic environments. This approach to sea louse control has environmental benefits and is cost-effective. The range of possible pathogens of lice is reviewed and epibionts recorded from sea lice, including the monogenean Udonella caligorum and ciliates, are examined. Baculoviruses when ingested by insects form occlusion bodies resulting in severe damage to the digestive system and subsequent death, and this may be a promising approach. Cleaner wrasse (Labridae) have been stocked commercially with farmed salmon since 1989, and recent work on improving the method is reviewed. Wrasse are sourced from a wild fishery and stocked at ratios of 1 to 25-150 salmon. Over 5 million wrasse are stocked annually in Norway and c 30% of smolts in Scotland were stocked with wrasse until 1998, when an outbreak of infections salmon anaemia (ISA) deterred many farmers from transferring wild fish to cages. A case study is given showing that salmon in cages stocked with wrasse had a burden of one to eight lice through the first year compared with up to 40 lice per fish on unprotected and untreated fish. Electivity indices were used to compare the relative composition of lice developmental stages on salmon in stocked and unstocked cages, and adult male and female lice were found to comprise only 6% of the population in cages with wrasse, compared with 49% adults on fish in control cages. Measures to improve the efficacy of wrasse as a way of cleaning salmon in the second production year include the use of refuges to assist over-wintering survival, and stocking ballan wrasse. Health hygiene includes sourcing wrasse in the farm locality, testing for pathogens, vaccination of wrasse and ultimately rearing wrasse for stocking. The role of wrasse in an IPM strategy is described.