Circular Single-stranded DNA Viruses Research Articles

Characterization of a complete genome of a circular single-stranded DNA virus from porcine stools in Korea

Porcine circular single-stranded DNA viruses have been just identified from swine feces in Korea. This virus was mentioned as bovine stool-associated circular DNA virus (BoSCV)-like virus discovered from porcine stools. However, the thorough characteristics of the virus were not identified. Therefore, this research focuses on finding a full genome sequence and analyzing the genetic features of the virus. The virus, now called porcine stool-associated circular DNA virus in Korea (PoSCV Kor), consists of 2,589 bases forming circular structure. It has two major ORFs inversely encoding replicase and capsid protein, with each stem-loop structure between 5' ends and 3' ends of the two putative ORFs. This characteristics is the same as PoSCV in New Zealand, but different from chimpanzee stool-associated circular virus (ChiSCVs) and BoSCV, which have one stem-loop structure. Therefore, it would be sure that PoSCV Kor is very similar to PoSCV in respect to the genetic aspect; the same number of nucleotide bases and the amino acid identity of replicase and capsid protein (96 and 93 %, respectively). This fact could be certified through the finding that PoSCV Kor and PoSCV are in the same cluster by phylogenetic analysis based on the comparison with full-sequences of other circular ssDNA viruses.

Detection of porcine anelloviruses in pork meat and human faeces

Torque teno viruses (TTV) are icosahedral, single-stranded circular DNA viruses infecting several vertebrate species. Currently, these viruses are considered non-pathogenic although they are suggested to be co-factors in several diseases. Recently single-stranded circular DNA viruses have been found in human faeces. Considering the consumption of pork meat products and the ubiquitous nature of swine TTV (Torque tenosus virus, TTSuV), the human population is frequently exposed to these viruses. To determine if TTSuVs could be delivered through food, human faecal samples were analysed for their presence. Indeed, the results of this study show that up to 25% of faecal samples were positive for known TTSuVs by PCR and sequencing. Additionally, all commercially available pork products purchased in Spanish supermarkets contained DNA of TTSuV.

Potential role of viruses in white plague coral disease

White plague (WP)-like diseases of tropical corals are implicated in reef decline worldwide, although their etiological cause is generally unknown. Studies thus far have focused on bacterial or eukaryotic pathogens as the source of these diseases; no studies have examined the role of viruses. Using a combination of transmission electron microscopy (TEM) and 454 pyrosequencing, we compared 24 viral metagenomes generated from Montastraea annularis corals showing signs of WP-like disease and/or bleaching, control conspecific corals, and adjacent seawater. TEM was used for visual inspection of diseased coral tissue. No bacteria were visually identified within diseased coral tissues, but viral particles and sequence similarities to eukaryotic circular Rep-encoding single-stranded DNA viruses and their associated satellites (SCSDVs) were abundant in WP diseased tissues. In contrast, sequence similarities to SCSDVs were not found in any healthy coral tissues, suggesting SCSDVs might have a role in WP disease. Furthermore, Herpesviridae gene signatures dominated healthy tissues, corroborating reports that herpes-like viruses infect all corals. Nucleocytoplasmic large DNA virus (NCLDV) sequences, similar to those recently identified in cultures of Symbiodinium (the algal symbionts of corals), were most common in bleached corals. This finding further implicates that these NCLDV viruses may have a role in bleaching, as suggested in previous studies. This study determined that a specific group of viruses is associated with diseased Caribbean corals and highlights the potential for viral disease in regional coral reef decline.

Discovery of Sclerotinia sclerotiorum Hypovirulence-Associated Virus-1 in Urban River Sediments of Heathcote and Styx Rivers in Christchurch City, New Zealand

In samples of benthic and bank river sediments of two urban rivers in Christchurch city (New Zealand), we identified and recovered isolates of Sclerotinia sclerotiorum hypovirulence-associated virus-1 (SsHADV-1), a fungus-infecting circular single-stranded DNA virus. This is the first report of SsHADV-1 outside of China and in environmental samples.

Research progress on phenomenon and biological control potential of hypovirulence in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum(Lib.) de Bary is a worldwide pathogenic fungus.It is difficult to control due to the lack of resistant plant lines,wide range of hosts and chemical fungicides resistance.S.sclerotiorum isolates have various pathogenicity.Some hypovirulent strains have been identified.This paper summarized the mycoviruses infecting S.sclerotiorum including RNA virus(SsDRV),single-stranded circular DNA virus(SsHADV-1) and some undetermined double-stranded RNA(dsRNA) factors.The transmission path of the mycovirus was explained.The way to break the mycelium incompatibility boundary was reviewed for effective spread of mycovirus between mycelium.New ideas and clues for future prevention and biological control of S.sclerotiorum were discussed.

New Volvovirus Isolates from Acheta domesticus (Japan) and Gryllus assimilis (United States)

A novel circular single-stranded DNA (ssDNA) virus, volvovirus, from the house cricket has been described recently. Here, we report the isolation of volvoviruses from Acheta domesticus in Japan and Gryllus assimilis in the United States. These Acheta domesticus volvovirus (AdVVV) isolates have genomes of 2,517 and 2,516 nucleotides (nt) and 4 large open reading frames (ORFs).

A divergent clade of circular single-stranded DNA viruses from pig feces

Using metagenomics and molecular cloning methods, we characterized five novel small, circular viral genomes from pig feces that are distantly related to chimpanzee and porcine stool-associated circular viruses, (ChiSCV and PoSCV1). Phylogenetic analysis placed these viruses into a highly divergent clade of this rapidly growing new viral family. This new clade of viruses, provisionally named porcine stool-associated circular virus 2 and 3 (PoSCV2 and PoSCV3), encodes a stem–loop structure (presumably the origin of DNA replication) in the small intergenic region and a replication initiator protein commonly found in other biological systems that replicate their genomes via the rolling–circle mechanism. Furthermore, these viruses also exhibit three additional overlapping open reading frames in the large intergenic region between the capsid and replication initiator protein genes.

A genome-wide pairwise-identity-based proposal for the classification of viruses in the genus Mastrevirus (family Geminiviridae)

Recent advances in the ease with which the genomes of small circular single-stranded DNA viruses can be amplified, cloned, and sequenced have greatly accelerated the rate at which full genome sequences of mastreviruses (family Geminiviridae, genus Mastrevirus) are being deposited in public sequence databases. Although guidelines currently exist for species-level classification of newly determined, complete mastrevirus genome sequences, these are difficult to apply to large sequence datasets and are permissive enough that, effectively, a high degree of leeway exists for the proposal of new species and strains. The lack of a standardised and rigorous method for testing whether a new genome sequence deserves such a classification is resulting in increasing numbers of questionable mastrevirus species proposals. Importantly, the recommended sequence alignment and pairwise identity calculation protocols of the current guidelines could easily be modified to make the classification of newly determined mastrevirus genome sequences significantly more objective. Here, we propose modified versions of these protocols that should substantially minimise the degree of classification inconsistency that is permissible under the current system. To facilitate the objective application of these guidelines for mastrevirus species demarcation, we additionally present a user-friendly computer program, SDT (species demarcation tool), for calculating and graphically displaying pairwise genome identity scores. We apply SDT to the 939 full genome sequences of mastreviruses that were publically available in May 2012, and based on the distribution of pairwise identity scores yielded by our protocol, we propose mastrevirus species and strain demarcation thresholds of >78 % and >94 % identity, respectively.

Designing of putative siRNA against geminiviral suppressors of RNAi to develop geminivirus-resistant papaya crop

Geminiviruses are single-stranded circular DNA viruses causing leaf curl disease in papaya crop. Post-Transcriptional Gene Silencing (PTGS), also known as RNAi, acts as a natural antiviral defence mechanism and plays a role in genome maintenance and development in plants. PTGS suppression by viruses makes the plant RNA silencing machinery inefficient. Three geminiviral genes namely AV2, AC2 and AC4 are found to play the role in suppression of RNA silencing. siRNA degrades the target mRNA in a homology-dependent manner. In-silico designing of siRNA against these three genes of geminiviruses infecting Carica papaya was done using bioinformatics tools. This strategy may provide PTGS by specifically targeting the viral genes involved in suppression of plant RNA silencing machinery.

Discovery of a novel circular single-stranded DNA virus from porcine faeces

A large number of novel single-stranded DNA (ssDNA) viruses have been characterised from various environmental sources in the last 5 years. The bulk of these have been from faecal sources, and faecal sampling is an ideal non-invasive pathogen sampling method. We characterised a novel ssDNA from a porcine faecal sample from Cass Basin of the South Island of New Zealand. The novel viral genome has two large open reading frames (ORFs), which are bidirectionally transcribed and separated by intergenic regions. The largest ORF has some degree of similarity (<30 %) to the putative capsid protein of chimpanzee stool-associated circular ssDNA virus (ChiSCV) and pig stool-associated single-stranded DNA virus (PigSCV), whereas the second-largest ORF has high similarity to the putative replication-associated protein (Rep) of ChiSCV (~50 %) and bovine stool-associated circular DNA virus (BoSCV; ~30 %). Based on genome architecture, location of putative stem-loop like elements, and maximum-likelihood phylogenetic analysis of the gene encoding the Rep protein, the novel isolate belongs to the same family of ssDNA viruses as ChiSCV and BoSCV.

Erratum to: A field guide to eukaryotic circular single-stranded DNA viruses: insights gained from metagenomics

Erratum to: A field guide to eukaryotic circular single-stranded DNA viruses: insights gained from metagenomics

A field guide to eukaryotic circular single-stranded DNA viruses: insights gained from metagenomics

Despite their small size and limited protein-coding capacity, the rapid evolution rates of single-stranded DNA (ssDNA) viruses have led to their emergence as serious plant and animal pathogens. Recently, metagenomics has revealed an unprecedented diversity of ssDNA viruses, expanding their known environmental distributions and host ranges. This review summarizes and contrasts the basic characteristics of known circular ssDNA viral groups, providing a resource for analyzing the wealth of ssDNA viral sequences identified through metagenomics. Since ssDNA viruses are largely identified based on conserved rolling circle replication proteins, this review highlights distinguishing motifs and catalytic residues important for replication. Genomes identified through metagenomics have demonstrated unique ssDNA viral genome architectures and revealed characteristics that blur the boundaries between previously well-defined groups. Metagenomic discovery of ssDNA viruses has created both a challenge to current taxonomic classification schemes and an opportunity to revisit hypotheses regarding the evolutionary history of these viruses.

Rescue of a Porcine Anellovirus (Torque Teno Sus Virus 2) from Cloned Genomic DNA in Pigs

Anelloviruses are a group of single-stranded circular DNA viruses infecting humans and other animal species. Animal models combined with reverse genetic systems of anellovirus have not been developed. We report here the construction and initial characterization of full-length DNA clones of a porcine anellovirus, torque teno sus virus 2 (TTSuV2), in vitro and in vivo. We first demonstrated that five cell lines, including PK-15 cells, are free of TTSuV1 or TTSuV2 contamination, as determined by a real-time PCR and an immunofluorescence assay (IFA) using anti-TTSuV antibodies. Recombinant plasmids harboring monomeric or tandem-dimerized genomic DNA of TTSuV2 from the United States and Germany were constructed. Circular TTSuV2 genomic DNA with or without introduced genetic markers and tandem-dimerized TTSuV2 plasmids were transfected into PK-15 cells, respectively. Splicing of viral mRNAs was identified in transfected cells. Expression of TTSuV2-specific open reading frame 1 (ORF1) in cell nuclei, especially in nucleoli, was detected by IFA. However, evidence of productive TTSuV2 infection was not observed in 12 different cell lines transfected with the TTSuV2 DNA clones. Transfection with circular DNA from a TTSuV2 deletion mutant did not produce ORF1 protein, suggesting that the observed ORF1 expression is driven by TTSuV2 DNA replication in cells. Pigs inoculated with either the tandem-dimerized clones or circular genomic DNA of U.S. TTSuV2 developed viremia, and the introduced genetic markers were retained in viral DNA recovered from the sera of infected pigs. The availability of an infectious DNA clone of TTSuV2 will facilitate future study of porcine anellovirus pathogenesis and biology.

Efficient Production of Porcine Circovirus Type 2 Capsid Protein using Baculovirus

Porcine circovirus type 2 (PCV2) is a single-stranded circular DNA virus associated with Postweaning multisystemic wasting syndrome (PMWS), which is considered to be an important infectious swine viral disease. PCV2 capsid protein encoded by ORF2 is a structural protein and expected as the high immunogenicity protein. In this study, we generated recombinant baculovirus containing ORF2 of PCV2 and analyzed the optimal conditions for the production of capsid protein in insect cell. Production and status of recombinant capsid protein in insect cell were confirmed by SDS-PAGE and Western blot analysis using His tag antibody and anti-PCV2 serum. The yield of recombinant capsid protein was high like as shown visible on SDS-PAGE. Optimal multiplicity of infection (MOI) and infection time of recombinant virus were determined as 5 MOI and 4 days, respectively. ORF2 is known to have N-linked glycosylation site, but we couldn't detect the glycosylation of recombinant protein in insect cells.

First time molecular detection and phylogenetic relationships of torque teno sus virus 1 and 2 in domestic pigs in Uganda: further evidence for a global distribution

BackgroundTorque teno sus virus 1 (TTSuV1) and 2 (TTSuV2) are small, single-stranded circular DNA viruses belonging to the Anelloviridae family. Available studies clearly show that both viruses are widely distributed in the pig populations in America, Europe and Asia, although the impact of the infection is still unclear. Currently, the situation in domestic pig populations on the African continent is not known. Therefore, the aim of this study was to investigate the possible presence of the two viruses in domestic pigs in Uganda, and describe the phylogenetic relationships to those in the rest of the world.ResultsNinety-five serum samples from six districts in Uganda were used, and PCR using TTSuV1 and 2 specific primers for the UTR region was run for viral nucleic acid detection. The positive samples were sequenced, and phylogenetic analyses performed in order to compare the Ugandan sequences with sequences from other parts of the world. The prevalence of TTSuV1 and 2 in the selected domestic pigs were estimated at 16.8% and 48.4% respectively, with co-infection found in 13.7%. The sequence identity was 90-100% between the Ugandan TTSuV1; and 63-100% between the Ugandan TTSuV2 sequences.ConclusionThis is the first report on the presence of TTSuV1 and 2 in domestic pigs in Uganda. These results highlight the importance of screening for emerging viruses given the globalisation of human activities.

Torque Teno Sus Virus in Pigs: an Emerging Pathogen?

The newly established family Anelloviridae includes a number of viruses infecting humans (Torque teno viruses) and other animal species. The ones infecting domestic swine and wild boar are nowadays named Torque teno sus viruses (TTSuV), which are small circular single-stranded DNA viruses highly prevalent in the pig population. So far, two genetically distinct TTSuV species are infecting swine. Both TTSuVs appear to efficiently spread by vertical and horizontal transmission routes; in fact, foetuses may be infected and the prevalence and viral loads increase by age of the animals. Detailed immunological studies on TTSuVs are still lacking, but it seems that there are no efficient immunological responses limiting viraemia. These viruses are currently receiving more attention due to the latest results on disease association. Torque teno sus viruses have been circulating unnoticed in pigs for a long time, and even considered non-pathogenic by themselves; there is increasing evidence that points to influence the development of some diseases or even affect their outcome. Such link has been mainly established with porcine circovirus diseases.

Instability in vitro of a PCV2 infectious clone containing an insertion between ORF1 and ORF2

Porcine circovirus 2 (PCV2) is a small circular single-stranded DNA virus that causes postweaning multisystemic wasting syndrome in pigs. We obtained an infectious clone, derived from PCV2 strain 1147 (size 1,767 bp), with a 60 bp insertion in the cap-rep intergenic region at the 3' end of the rep. In vitro propagation and sequencing of virus showed mixed sequence for the cap-rep intergenic region. Cloning of this region of virus from the passages 2 and 20 showed deletions of various size of the 60 bp insertion. Viruses from the passage 20 showed deletions of the 60 bp insertion and had extra (+1 to +5) or less (-1 or -2) bp in the intergenic region as compared to 1,147. These findings suggest that insertion of a 60-bp DNA sequence at the 3' end of the rep is unstable in vitro. This finding can have implications for the genetic engineering of PCV2.

Widespread Horizontal Gene Transfer from Circular Single-stranded DNA Viruses to Eukaryotic Genomes

BackgroundIn addition to vertical transmission, organisms can also acquire genes from other distantly related species or from their extra-chromosomal elements (plasmids and viruses) via horizontal gene transfer (HGT). It has been suggested that phages represent substantial forces in prokaryotic evolution. In eukaryotes, retroviruses, which can integrate into host genome as an obligate step in their replication strategy, comprise approximately 8% of the human genome. Unlike retroviruses, few members of other virus families are known to transfer genes to host genomes.ResultsHere we performed a systematic search for sequences related to circular single-stranded DNA (ssDNA) viruses in publicly available eukaryotic genome databases followed by comprehensive phylogenetic analysis. We conclude that the replication initiation protein (Rep)-related sequences of geminiviruses, nanoviruses and circoviruses have been frequently transferred to a broad range of eukaryotic species, including plants, fungi, animals and protists. Some of the transferred viral genes were conserved and expressed, suggesting that these genes have been coopted to assume cellular functions in the host genomes. We also identified geminivirus-like and parvovirus-like transposable elements in genomes of fungi and lower animals, respectively, and thereby provide direct evidence that eukaryotic transposons could derive from ssDNA viruses.ConclusionsOur discovery extends the host range of circular ssDNA viruses and sheds light on the origin and evolution of these viruses. It also suggests that ssDNA viruses act as an unforeseen source of genetic innovation in their hosts.

Leukogram abnormalities in gnotobiotic pigs infected with porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a single-stranded circular DNA virus that is the causative agent of porcine circovirus associated disease (PCVAD), a disease complex affecting swine around the world. Although this virus is believed to negatively affect the host's immune system, the mechanism by which PCV2 induces disease is not completely understood. This report describes a series of PCV2 experiments using the gnotobiotic pig model in which a relationship was demonstrated between abnormal leukograms and development of clinical disease in PCV2-infected pigs. When compared to control pigs the leukogram was characterized by a decrease in lymphocytes within 14 days post inoculation (dpi) followed by an increase in neutrophils 7–14 days later. No significant changes in the circulating monocyte, basophil, and eosinophil cell populations were detected. The combination of an absolute neutrophilia and lymphopenia produced a neutrophil/lymphocyte ratio that was predictive of clinical disease and was inversely correlated with the presence of neutralizing antibodies. Based on previous reports, the lymphopenia may be attributed to a direct cytolytic effect of the virus and could negatively affect the pig's immune response. The role of the neutrophilia in the pathogenesis of PCVAD in gnotobiotic pigs is unknown.

The prevalence of transfusion-transmitted virus (TTV) infection in patients with chronic hepatitis B and C in southwest of Iran

Transfusion-transmitted virus (TTV) is an unenveloped circular single-stranded DNA virus with a diameter of 30 to 32 nm that was first described in 1997 in Japan. TTV was detected in various populations without proven pathology, including blood donors and in patients with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV). The aim of this study was to determine the prevalence of TTV DNA in patients with chronic hepatitis B and C in southwest Iran. Viral TTV-DNA was studied in 442 samples (202 with HBV, 138 with HCV and 102 controls) collected from southwest of Iran. All the extracted serum DNA was amplified by TTV ORF1 gene specific primers using the semi nested polymerase chain reaction (PCR) technique. TTV DNA was detected in the serum of 8.9 and 10.8% patients with chronic hepatitis B and C, respectively. The prevalence of TTV-DNA in the serum of the 102 controls was 2.9%. The results showed significant relationship of TTV with HBV and HCV in patients from T test examination (P < 0.01). The prevalence of TTV-DNA in Iranian hepatitis B and C patients was rather high when compared with those of other countries. To control and prevent the distribution of TT-virus, examination of the blood and blood products seems necessary. Key words : Transfusion-transmitted virus (TTV), hepatitis C virus (HCV), hepatitis B virus (HBV), ORF1 gene, semi nested polymerase chain reaction (PCR), Iran.