Search

Simple Summary: Most insect species, like most other animal species, host a number of different viruses, and because the number of insect species are so great, the diversity of viruses in insects is expected to be larger than in any other animal lineage. Despite this expectation, few studies are conducted to characterize such viruses and fewer still are carried out to describe the evolutionary dynamics between host and virus. Here we studied a virus that infects an agriculturally important moth species corn earworm (Helicoverpa zea) by comparing host and viral genomes. From this comparison it was found that the virus has incorporated several host genes among which the gene cytosolic serine hydroxymethyltransferase is not known from any other virus and thus may provide a unique study system for better understanding the function of this gene. Additionally, undescribed genes were found in both the virus and host that possess sequences originating from bacteria. Lastly the prevalence of the virus was tested across a broad geographic range and found to be present in nearly all host populations tested. Given these findings, more studies should be initiated to characterize insect viruses for novel molecular interactions with possible uses in gene editing and insect biological control. Insect viruses have been described from numerous lineages, yet patterns of genetic exchange and viral prevalence, which are essential to understanding host–virus coevolution, are rarely studied. In Helicoverpa zea, the virus HzNV-2 can cause deformity of male and female genitalia, resulting in sterility. Using ddPCR, we found that male H. zea with malformed genitalia (agonadal) contained high levels of HzNV-2 DNA, confirming previous work. HzNV-2 was found to be prevalent throughout the United States, at more than twice the rate of the baculovirus HaSNPV, and that it contained several host-acquired DNA sequences. HzNV-2 possesses four recently endogenized lepidopteran genes and several more distantly related genes, including one gene with a bacteria-like sequence found in both host and virus. Among the recently acquired genes is cytosolic serine hydroxymethyltransferase (cSHMT). In nearly all tested H. zea, cSHMT contained a 200 bp transposable element (TE) that was not found in cSHMT of the sister species H. armigera. No other virus has been found with host cSHMT, and the study of this shared copy, including possible interactions, may yield new insights into the function of this gene with possible applications to insect biological control, and gene editing. [ABSTRACT FROM AUTHOR]

Soils impact global carbon cycling and their resident microbes are critical to their biogeochemical processing and ecosystem outputs. Based on studies in marine systems, viruses infecting soil microbes likely modulate host activities via mortality, horizontal gene transfer, and metabolic control. However, their roles remain largely unexplored due to technical challenges with separating, isolating, and extracting DNA from viruses in soils. Some of these challenges have been overcome by using whole genome amplification methods and while these have allowed insights into the identities of soil viruses and their genomes, their inherit biases have prevented meaningful ecological interpretations. Here we experimentally optimized steps for generating quantitatively-amplified viral metagenomes to better capture both ssDNA and dsDNA viruses across three distinct soil habitats along a permafrost thaw gradient. First, we assessed differing DNA extraction methods (PowerSoil, Wizard mini columns, and cetyl trimethylammonium bromide) for quantity and quality of viral DNA. This established PowerSoil as best for yield and quality of DNA from our samples, though ∼1/3 of the viral populations captured by each extraction kit were unique, suggesting appreciable differential biases among DNA extraction kits. Second, we evaluated the impact of purifying viral particles after resuspension (by cesium chloride gradients; CsCl) and of viral lysis method (heat vs bead-beating) on the resultant viromes. DNA yields after CsCl particle-purification were largely non-detectable, while unpurified samples yielded 1-2-fold more DNA after lysis by heat than by bead-beating. Virome quality was assessed by the number and size of metagenome-assembled viral contigs, which showed no increase after CsCl-purification, but did from heat lysis relative to bead-beating. We also evaluated sample preparation protocols for ssDNA virus recovery. In both CsCl-purified and non-purified samples, ssDNA viruses were successfully recovered by using the Accel-NGS 1S Plus Library Kit. While ssDNA viruses were identified in all three soil types, none were identified in the samples that used bead-beating, suggesting this lysis method may impact recovery. Further, 13 ssDNA vOTUs were identified compared to 582 dsDNA vOTUs, and the ssDNA vOTUs only accounted for ∼4% of the assembled reads, implying dsDNA viruses were dominant in these samples. This optimized approach was combined with the previously published viral resuspension protocol into a sample-to-virome protocol for soils now available at protocols.io, where community feedback creates 'living' protocols. This collective approach will be particularly valuable given the high physicochemical variability of soils, which will may require considerable soil type-specific optimization. This optimized protocol provides a starting place for developing quantitatively-amplified viromic datasets and will help enable viral ecogenomic studies on organic-rich soils.

Insect viruses have been described from numerous lineages, yet patterns of genetic exchange and viral prevalence, which are essential to understanding host–virus coevolution, are rarely studied. In Helicoverpa zea, the virus HzNV-2 can cause deformity of male and female genitalia, resulting in sterility. Using ddPCR, we found that male H. zea with malformed genitalia (agonadal) contained high levels of HzNV-2 DNA, confirming previous work. HzNV-2 was found to be prevalent throughout the United States, at more than twice the rate of the baculovirus HaSNPV, and that it contained several host-acquired DNA sequences. HzNV-2 possesses four recently endogenized lepidopteran genes and several more distantly related genes, including one gene with a bacteria-like sequence found in both host and virus. Among the recently acquired genes is cytosolic serine hydroxymethyltransferase (cSHMT). In nearly all tested H. zea, cSHMT contained a 200 bp transposable element (TE) that was not found in cSHMT of the sister species H. armigera. No other virus has been found with host cSHMT, and the study of this shared copy, including possible interactions, may yield new insights into the function of this gene with possible applications to insect biological control, and gene editing.

Double-stranded DNA viruses of the realm Varidnaviria (formerly PRD1-adenovirus lineage) are characterized by homologous major capsid proteins (MCPs) containing one (kingdom: Helvetiavirae) or two β-barrel domains (kingdom: Bamfordvirae) known as the jelly roll folds. Most of them also share homologous packaging ATPases (pATPases). Remarkably, Varidnaviria infect hosts from the three domains of life, suggesting that these viruses could be very ancient and share a common ancestor. Here, we analyzed the evolutionary history of Varidnaviria based on single and concatenated phylogenies of their MCPs and pATPases. We excluded Adenoviridae from our analysis as their MCPs and pATPases are too divergent. Sphaerolipoviridae, the only family in the kingdom Helvetiavirae, exhibit a complex history: their MCPs are very divergent from those of other Varidnaviria, as expected, but their pATPases groups them with Bamfordvirae. In single and concatenated trees, Bamfordvirae infecting archaea were grouped with those infecting bacteria, in contradiction with the cellular tree of life, whereas those infecting eukaryotes were organized into three monophyletic groups: the Nucleocytoviricota phylum, formerly known as the Nucleo-Cytoplasmic Large DNA Viruses (NCLDVs), Lavidaviridae (virophages) and Polintoviruses. Although our analysis mostly supports the recent classification proposed by the International Committee on Taxonomy of Viruses (ICTV), it also raises questions, such as the validity of the Adenoviridae and Helvetiavirae ranking. Based on our phylogeny, we discuss current hypotheses on the origin and evolution of Varidnaviria and suggest new ones to reconcile the viral and cellular trees.

Double-stranded DNA viruses of the realm Varidnaviria (formerly PRD1-adenovirus lineage) are characterized by homologous major capsid proteins (MCPs) containing one (kingdom: Helvetiavirae) or two β-barrel domains (kingdom: Bamfordvirae) known as the jelly roll folds. Most of them also share homologous packaging ATPases (pATPases). Remarkably, Varidnaviria infect hosts from the three domains of life, suggesting that these viruses could be very ancient and share a common ancestor. Here, we analyzed the evolutionary history of Varidnaviria based on single and concatenated phylogenies of their MCPs and pATPases. We excluded Adenoviridae from our analysis as their MCPs and pATPases are too divergent. Sphaerolipoviridae , the only family in the kingdom Helvetiavirae , exhibit a complex history: their MCPs are very divergent from those of other Varidnaviria , as expected, but their pATPases groups them with Bamfordvirae. In single and concatenated trees, Bamfordvirae infecting archaea were grouped with those infecting bacteria, in contradiction with the cellular tree of life, whereas those infecting eukaryotes were organized into three monophyletic groups: the Nucleocytoviricota phylum, formerly known as the Nucleo-Cytoplasmic Large DNA Viruses (NCLDVs), Lavidaviridae (virophages) and Polintoviruses. Although our analysis mostly supports the recent classification proposed by the International Committee on Taxonomy of Viruses (ICTV), it also raises questions, such as the validity of the Adenoviridae and Helvetiavirae ranking. Based on our phylogeny, we discuss current hypotheses on the origin and evolution of Varidnaviria and suggest new ones to reconcile the viral and cellular trees. [ABSTRACT FROM AUTHOR]

Inspired by recent discoveries of the prevalence of large viruses in the environment, we reassessed the longstanding approach of filtering water through small-pore-size filters to separate viruses from cells before metagenomic analysis. We collected samples from three sites in Hamilton Harbour, an embayment of Lake Ontario, and studied 6 data sets derived from <0.45-μm-and>0.45-μm-size fractions to compare the diversity of viruses in these fractions. At the level of virus order/family, we observed highly diverse and distinct virus communities in the >0.45-μm-size fractions, whereas the <0.45-μm-size fractions were composed primarily of Caudovirales. The relative abundances of Caudovirales for which hosts could be inferred varied widely between size fractions, with higher relative abundances of cyanophages in the >0.45-μm-size fractions, potentially indicating replication within cells during ongoing infections. Many viruses of eukaryotes, such as Mimiviridae, Phycodnaviridae, Iridoviridae, and Poxviridae, were detected exclusively in the oftendisregarded >0.45-μm-size fractions. In addition to observing unique virus communities associated with each size fraction from every site we examined, we detected viruses common to both fractions, suggesting that these are candidates for further exploration because they could be the product of ongoing or recent lytic events. Most importantly, our observations indicate that analysis of either fraction alone provides only a partial perspective of double-stranded DNA (dsDNA) viruses in the environment, highlighting the need for more comprehensive approaches for analyzing virus communities inferred from metagenomic sequencing. [ABSTRACT FROM AUTHOR]

Mavericks are virus-like mobile genetic elements found in the genomes of eukaryotes. Although Mavericks encode capsid morphogenesis homologs, their viral particles have not been observed. Here, we provide new evidence supporting the viral nature of Mavericks and the potential existence of virions. To this end, we conducted a phylogenomic analysis of Mavericks in hundreds of vertebrate genomes, discovering 134 elements with an intact coding capacity in 17 host species. We reveal an extensive genomic fossil record in 143 species and date three groups of elements to the Late Cretaceous. Bayesian phylogenetic analysis using genomic fossil orthologs suggests that Mavericks have infected osteichthyans for ∼419 My. They have undergone frequent cross-species transmissions in cyprinid fish and all core genes are subject to strong purifying selection. We conclude that vertebrate Mavericks form an ancient lineage of aquatic dsDNA viruses which are probably still functional in some vertebrate lineages. [ABSTRACT FROM AUTHOR]

The key to a curative treatment of hepatitis B virus (HBV) infection is the eradication of the intranuclear episomal covalently closed circular DNA (cccDNA), the stable persistence reservoir of HBV. Currently, established therapies can only limit HBV replication but fail to tackle the cccDNA. Thus, novel therapeutic approaches toward curative treatment are urgently needed. Recent publications indicated a strong association between the HBV core protein SUMOylation and the association with promyelocytic leukemia nuclear bodies (PML-NBs) on relaxed circular DNA to cccDNA conversion. We propose that interference with the cellular SUMOylation system and PML-NB integrity using arsenic trioxide provides a useful tool in the treatment of HBV infection. Our study showed a significant reduction in HBV-infected cells, core protein levels, HBV mRNA, and total DNA. Additionally, a reduction, albeit to a limited extent, of HBV cccDNA could be observed. Furthermore, this interference was also applied for the treatment of an established HBV infection, characterized by a stably present nuclear pool of cccDNA. Arsenic trioxide (ATO) treatment not only changed the amount of expressed HBV core protein but also induced a distinct relocalization to an extranuclear phenotype during infection. Moreover, ATO treatment resulted in the redistribution of transfected HBV core protein away from PML-NBs, a phenotype similar to that previously observed with SUMOylation-deficient HBV core. Taken together, these findings revealed the inhibition of HBV replication by ATO treatment during several steps of the viral replication cycle, including viral entry into the nucleus as well as cccDNA formation and maintenance. We propose ATO as a novel prospective treatment option for further pre-clinical and clinical studies against HBV infection., Importance: The main challenge for the achievement of a functional cure for hepatitis B virus (HBV) is the covalently closed circular DNA (cccDNA), the highly stable persistence reservoir of HBV, which is maintained by further rounds of infection with newly generated progeny viruses or by intracellular recycling of mature nucleocapsids. Eradication of the cccDNA is considered to be the holy grail for HBV curative treatment; however, current therapeutic approaches fail to directly tackle this HBV persistence reservoir. The molecular effect of arsenic trioxide (ATO) on HBV infection, protein expression, and cccDNA formation and maintenance, however, has not been characterized and understood until now. In this study, we reveal ATO treatment as a novel and innovative therapeutic approach against HBV infections, repressing viral gene expression and replication as well as the stable cccDNA pool at low micromolar concentrations by affecting the cellular function of promyelocytic leukemia nuclear bodies., Competing Interests: U.P. is a co-founder and shareholder of SCG Cell Therapy and received personal fees as a speaker or an ad hoc scientific advisor from AbbVie, Aligos, Arbutus, Biontech, Gilead, GSK, Leukocare, J&J, Roche, Sanofi, Sobi, Vaccitech, and VIR Biotechnology. The other authors declare no competing interests.

Natural isolates of baculoviruses (as well as other dsDNA viruses) generally consist of homogenous or heterogenous populations of genotypes. The number and positions of single nucleotide polymorphisms (SNPs) from sequencing data are often used as suitable markers to study their genotypic composition. Identifying and assigning the specificities and frequencies of SNPs from high-throughput genome sequencing data can be very challenging, especially when comparing between several sequenced isolates or samples. In this study, the new tool “bacsnp”, written in R programming langue, was developed as a downstream process, enabling the detection of SNP specificities across several virus isolates. The basis of this analysis is the use of a common, closely related reference to which the sequencing reads of an isolate are mapped. Thereby, the specificities of SNPs are linked and their frequencies can be used to analyze the genetic composition across the sequenced isolate. Here, the downstream process and analysis of detected SNP positions is demonstrated on the example of three baculovirus isolates showing the fast and reliable detection of a mixed sequenced sample.

Viruses are the most prevalent infectious agents, populating almost every ecosystem on earth. Most viruses carry only a handful of genes supporting their replication and the production of capsids. It came as a great surprise in 2003 when the first giant virus was discovered and found to have a >1 Mbp genome encoding almost a thousand proteins. Following this first discovery, dozens of giant virus strains across several viral families have been reported. Here, we provide an updated quantitative and qualitative view on giant viruses and elaborate on their shared and variable features. We review the complexity of giant viral proteomes, which include functions traditionally associated only with cellular organisms. These unprecedented functions include components of the translation machinery, DNA maintenance, and metabolic enzymes. We discuss the possible underlying evolutionary processes and mechanisms that might have shaped the diversity of giant viruses and their genomes, highlighting their remarkable capacity to hijack genes and genomic sequences from their hosts and environments. This leads us to examine prominent theories regarding the origin of giant viruses. Finally, we present the emerging ecological view of giant viruses, found across widespread habitats and ecological systems, with respect to the environment and human health.

Marek’s disease (MD), caused by Marek’s disease virus (MDV), a poultry-borne alphaherpesvirus, is a devastating disease of poultry causing an estimated annual loss of one billion dollars to poultry producers, worldwide. Despite decades of control through vaccination, MDV field strains continue to emerge having increased virulence. The evolutionary mechanism driving the emergence of this continuum of strains to increased MDV virulence, however, remains largely enigmatic. Increase in MDV virulence has been associated with specific amino acid changes within the C-terminus domain of Mareks’s EcoRI-Q (meq)-encoded oncoprotein. In this study, we sought to determine whether the meq gene has evolved adaptively and whether past vaccination efforts have had any significant effect on the reduction or increase of MDV diversity over time. Our analysis suggests that meq is estimated to be evolving at a much faster rate than most dsDNA viruses, and is comparable with the evolutionary rate of RNA viruses. Interestingly, most of the polymorphisms in meq gene appear to have evolved under positive selection and the time of divergence at the meq locus coincides with the period during which the poultry industry had undergone transitions in management practices including the introduction and widespread use of live attenuated vaccines. Our study has revealed that the decades-long use of vaccines did not reduce MDV diversity, but rather had a stimulating effect on the emergence of field strains with increased genetic diversity until the early 2000s. During the years 2004–2005, there was an abrupt decline in the genetic diversity of field isolates followed by a recovery from this bottleneck in the year 2010. Collectively, these data suggest that vaccination seems to not have had any effect on MDV eradication, but rather had a stimulating effect on MDV emergence through adaptation. [ABSTRACT FROM AUTHOR]

Background: The nucleotide analogue brincidofovir was developed to prevent and treat infections caused by double-stranded DNA viruses. Based on in vitro data suggesting an antiviral effect against Ebola virus, brincidofovir was included in the World Health Organisation list of agents that should be prioritised for clinical evaluation in patients with Ebola virus disease (EVD) during the West African epidemic. Methods and Findings: In this single-arm phase 2 trial conducted in Liberia, patients with laboratory-confirmed EVD (two months of age or older, enrolment bodyweight ≥50 kg) received oral brincidofovir 200 mg as a loading dose on day 0, followed by 100 mg brincidofovir on days 3, 7, 10, and 14. Bodyweight-adjusted dosing was used for patients weighing <50 kg at enrolment. The primary outcome was survival at Day 14 after the first dose of brincidofovir. Four patients were enrolled between 01 January 2015 and 31 January 2015. The trial was stopped following the decision by the manufacturer to terminate their program of development of brincidofovir for EVD. No Serious Adverse Reactions or Suspected Unexpected Serious Adverse Reactions were identified. All enrolled subjects died of an illness consistent with EVD. Conclusions: Due to the small sample size it was not possible to determine the efficacy of brincidofovir for the treatment of EVD. The premature termination of the trial highlights the need to establish better practices for preclinical in-vitro and animal screening of therapeutics for potentially emerging epidemic infectious diseases prior to their use in patients. Trial Registration: Pan African Clinical Trials Registry [ABSTRACT FROM AUTHOR]

The application of CRISPR/Cas9 to improve genome engineering efficiency for large dsDNA viruses has been extensively described, but a robust and versatile method for high-throughput generation of marker-free recombinants for a desired locus has not yet been reported. Cytoplasmic-replicating viruses use their own repair enzymes for homologous recombination, while nuclear-replicating viruses use the host repair machinery. This is translated into a wide range of Cas9-induced homologous recombination efficiencies, depending on the virus replication compartment and viral/host repair machinery characteristics and accessibility. However, the use of Cas9 as a selection agent to target parental virus genomes robustly improves the selection of desired recombinants across large dsDNA viruses. We used ectromelia virus (ECTV) and herpes simplex virus (HSV) type 1 and 2 to optimize a CRISPR/Cas9 method that can be used versatilely for efficient genome editing and selection of both cytoplasmic- and nuclear-replicating viruses. We performed a genome-wide genetic variant analysis of mutations located at predicted off-target sequences for 20 different recombinants, showing off-target-free accuracy by deep sequencing. Our results support this optimized method as an efficient, accurate and versatile approach to enhance the two critical factors of high-throughput viral genome engineering: generation and colour-based selection of recombinants. This application of CRISPR/Cas9 reduces the time and labour for screening of desired recombinants, allowing for high-throughput generation of large collections of mutant dsDNA viruses for a desired locus, optimally in less than 2 weeks.

Natural isolates of baculoviruses (as well as other dsDNA viruses) generally consist of homogenous or heterogenous populations of genotypes. The number and positions of single nucleotide polymorphisms (SNPs) from sequencing data are often used as suitable markers to study their genotypic composition. Identifying and assigning the specificities and frequencies of SNPs from high-throughput genome sequencing data can be very challenging, especially when comparing between several sequenced isolates or samples. In this study, the new tool "bacsnp", written in R programming langue, was developed as a downstream process, enabling the detection of SNP specificities across several virus isolates. The basis of this analysis is the use of a common, closely related reference to which the sequencing reads of an isolate are mapped. Thereby, the specificities of SNPs are linked and their frequencies can be used to analyze the genetic composition across the sequenced isolate. Here, the downstream process and analysis of detected SNP positions is demonstrated on the example of three baculovirus isolates showing the fast and reliable detection of a mixed sequenced sample. [ABSTRACT FROM AUTHOR]

Viruses are the most prevalent infectious agents, populating almost every ecosystem on earth. Most viruses carry only a handful of genes supporting their replication and the production of capsids. It came as a great surprise in 2003 when the first giant virus was discovered and found to have a >1 Mbp genome encoding almost a thousand proteins. Following this first discovery, dozens of giant virus strains across several viral families have been reported. Here, we provide an updated quantitative and qualitative view on giant viruses and elaborate on their shared and variable features. We review the complexity of giant viral proteomes, which include functions traditionally associated only with cellular organisms. These unprecedented functions include components of the translation machinery, DNA maintenance, and metabolic enzymes. We discuss the possible underlying evolutionary processes and mechanisms that might have shaped the diversity of giant viruses and their genomes, highlighting their remarkable capacity to hijack genes and genomic sequences from their hosts and environments. This leads us to examine prominent theories regarding the origin of giant viruses. Finally, we present the emerging ecological view of giant viruses, found across widespread habitats and ecological systems, with respect to the environment and human health. [ABSTRACT FROM AUTHOR]

Despite very low sequence homology, the major capsid proteins of double-stranded DNA (dsDNA) bacteriophages, some archaeal viruses, and the herpesviruses share a structural motif, the HK97 fold. Bacteriophage P22, a paradigm for this class of viruses, belongs to a phage gene cluster that contains three homology groups: P22-like, CUS-3-like, and Sf6-like. The coat protein of each phage has an inserted domain (I-domain) that is more conserved than the rest of the coat protein. In P22, loops in the I-domain are critical for stabilizing intra- and intersubunit contacts that guide proper capsid assembly. The nuclear magnetic resonance (NMR) structures of the P22, CUS-3, and Sf6 I-domains reveal that they are all six-stranded, anti-parallel β-barrels. Nevertheless, significant structural differences occur in loops connecting the β-strands, in surface electrostatics used to dock the I-domains with their respective coat protein core partners, and in sequence motifs displayed on the capsid surfaces. Our data highlight the structural diversity of I-domains that could lead to variations in capsid assembly mechanisms and capsid surfaces adapted for specific phage functions. IMPORTANCE Comparative studies of protein structures often provide insights into their evolution. The HK97 fold is a structural motif used to form the coat protein shells that encapsidate the genomes of many dsDNA phages and viruses. The structure and function of coat proteins based on the HK97 fold are often embellished by the incorporation of I-domains. In the present work we compare I-domains from three phages representative of highly divergent P22-like homology groups. While the three I-domains share a six-stranded β-barrel skeleton, there are differences (i) in structure elements at the periphery of the conserved fold, (ii) in the locations of disordered loops important in capsid assembly and conformational transitions, (iii) in surfaces charges, and (iv) in sequence motifs that are potential ligand-binding sites. These structural modifications on the rudimentary I-domain fold suggest that considerable structural adaptability was needed to fulfill the versatile range of functional requirements for distinct phages., (Copyright © 2019 American Society for Microbiology.)