Fatty acid profiles of invertebrate iridescent viruses

A Systematic Review on Viruses in Mass-Reared Edible Insect Species

Edible insects are expected to become an important nutrient source for animals and humans in the Western world in the near future. Only a few studies on viruses in edible insects with potential for industrial rearing have been published and concern only some edible insect species. Viral pathogens that can infect insects could be non-pathogenic, or pathogenic to the insects themselves, or to humans and animals. The objective of this systematic review is to provide an overview of the viruses detected in edible insects currently considered for use in food and/or feed in the European Union or appropriate for mass rearing, and to collect information on clinical symptoms in insects and on the vector role of insects themselves. Many different virus species have been detected in edible insect species showing promise for mass production systems. These viruses could be a risk for mass insect rearing systems causing acute high mortality, a drastic decline in growth in juvenile stages and in the reproductive performance of adults. Furthermore, some viruses could pose a risk to human and animal health where insects are used for food and feed.

Invertebrate Iridoviruses: A Glance over the Last Decade

Members of the family Iridoviridae (iridovirids) are large dsDNA viruses that infect both invertebrate and vertebrate ectotherms and whose symptoms range in severity from minor reductions in host fitness to systemic disease and large-scale mortality. Several characteristics have been useful for classifying iridoviruses; however, novel strains are continuously being discovered and, in many cases, reliable classification has been challenging. Further impeding classification, invertebrate iridoviruses (IIVs) can occasionally infect vertebrates; thus, host range is often not a useful criterion for classification. In this review, we discuss the current classification of iridovirids, focusing on genomic and structural features that distinguish vertebrate and invertebrate iridovirids and viral factors linked to host interactions in IIV6 (Invertebrate iridescent virus 6). In addition, we show for the first time how complete genome sequences of viral isolates can be leveraged to improve classification of new iridovirid isolates and resolve ambiguous relations. Improved classification of the iridoviruses may facilitate the identification of genus-specific virulence factors linked with diverse host phenotypes and host interactions.

Lipidomic study of intracellular Singapore grouper iridovirus

Singapore grouper iridoviruses (SGIV) infected grouper cells release few enveloped extracellular viruses by budding and many unenveloped intracellular viruses following cell lysis. The lipid composition and function of such unenveloped intracellular viruses remain unknown. Detergent treatment of the intracellular viruses triggered the loss of viral lipids, capsid proteins and infectivity. Enzymatic digestion of the viral lipids with phospholipases and sphingomyelinase retained the viral capsid proteins but reduced infectivity. Over 220 lipid species were identified and quantified from the viruses and its producer cells by electrospray ionization mass spectrometry. Ten caspid proteins that dissociated from the viruses following the detergent treatments were identified by MALDI-TOF/TOF-MS/MS. Five of them were demonstrated to be lipid-binding proteins. This is the first research detailing the lipidome and lipid–protein interactions of an unenveloped virus. The identified lipid species and lipid-binding proteins will facilitate further studies of the viral assembly, egress and entry.

Sensitivity of Invertebrate iridescent virus 6 to organic solvents, detergents, enzymes and temperature treatment

The sensitivity of Invertebrate iridescent virus 6 (IIV-6) to a selection of organic solvents, detergents, enzymes and heat treatment was assayed in Spodoptera frugiperda (Sf9) cells and by injection of inoculum into larvae of Galleria mellonella. In several cases, the degree of sensitivity of the virus depended on the method of assay; cell culture assays indicated greater losses of activity than insect bioassay. IIV-6 was sensitive to chloroform but sensitivity to ether was only detected by cell culture assay. Sensitivity (defined as a reduction of at least 1 log activity) was detected following treatment by 1 and 0.1% SDS, 1% Triton-X100, 70% ethanol, 70% methanol, 1% sodium deoxycholate, pH 11.1 and 3.0. No sensitivity was detected to 1% Tween 80, 1 M MgCl2, 100 mM EDTA, lipase, phospholipase A2, proteinase K, or trypsin at the concentrations tested. Viral activity was reduced by approximately 4 logs following heating to 70 degrees C for 60 min or 80 degrees C for 30 min. The above observations highlight the need for studies on the role of the virus lipid component in the process of particle entry into cells, and may explain why vertebrate and invertebrate iridoviruses have been reported to differ in their sensitivity to organic solvents and enzymes.

Characterization of an iridescent virus isolated from Gryllus bimaculatus (Orthoptera: Gryllidae)

We have isolated an iridescent virus from commercially produced colonies of Gryllus bimaculatus in Germany, which showed apparent mortality. Transmission electron microscopy studies on adult cricket specimens revealed the paracrystalline assembly of icosahedral virus particles in the cytoplasm of hypertrophied abdominal fat body cells. The infecting agent could be cultivated in the lepidopteran cell line sf-9, where it caused cytopathogenic effects such as cell hypertrophy, cytoplasmic vacuolization, and cell death within 8 days postinfection. Infection titers of the first virus passage reached 10(7.5) TCID(50)/ml. Negatively stained virus particles (n = 100) had dimensions of 172 +/- 6 nm (apex to apex) and 148 +/- 5 nm (side to side). SDS-polyacrylamide gel electrophoresis of virus proteins showed more than 20 distinct polypeptides with a major species of approximately 50 kDa. Analysis of the restriction fragment length profiles from digestion of purified viral DNA with the endonucleases EcoRI, BamHI, and HindIII showed marked differences from the profiles of iridoviruses of lower vertebrates (genus Ranavirus), e.g., Rana esculenta Iridovirus and Frog virus 3. Restriction enzyme digests with the endonucleases MspI and HpaII indicated the lack of methylation of viral DNA. Polymerase chain reaction led to the amplification of a 420-bp gene fragment with 97% sequence homology to the major capsid protein gene of Chilo iridescent virus. These data indicate that this new isolate, which we propose to be termed Gryllus bimaculatus iridescent virus, belongs to the genus Iridovirus of the family Iridoviridae.