Biology subjects

Varsani, A.

Publications and source records attributed to Varsani, A..

18 recordsLinked to original sources

bioRxiv2026

Insights from a mobile healthcare clinic in Madagascar: Diversity and dynamics of viruses from febrile individuals in rural subsistence communities

Communities living in biodiversity hotspots are at increased risk of pathogen exposure and spread due to insufficient access to nutrition, clean water, and sanitation. Viruses, in particular, have high epidemic and spillover potential, and widespread health impacts, yet, viral diversity and dynamics remain understudied in many high-risk regions. In Madagascar, a hotspot with unparalleled biodiversity, socioeconomic constraints, and a heavy burden of infectious diseases, ongoing healthcare initiatives provide opportunities to survey circulating viral diversity. Here, we used a metagenomic workflow to characterize the viromes of oral/nasal swabs from febrile individuals visiting a mobile healthcare clinic in southeastern Madagascar, of which 49% were malaria-positive (Plasmodium falciparum). We characterized sequences of human-infecting viruses from twelve families (Adenoviridae, Anelloviridae, Orthoherpesviridae, Papillomaviridae, Polyomaviridae, Astroviridae, Coronaviridae, Matonaviridae, Orthomyxoviridae, Paramyxoviridae, Picornaviridae, and Sedoreoviridae). These viral sequences generally showed high similarity to known lineages circulating globally, but multiple viruses considered rare or emerging were identified (e.g. enterovirus C105, enterovirus C117). While we did not detect a significant association between malaria status and pathogenic virus presence, younger individuals had higher odds of having a pathogenic virus. Nonpathogenic viruses in Anelloviridae were prevalent and diverse with richness ranging from 0 to 70. Individuals with P. falciparum or a pathogenic virus tended to share more anelloviruses. We also detected viruses that are protist-associated, plant-infecting, or with unknown hosts. Overall, our work documents extensive viral diversity in Madagascar, highlighting how metagenomic workflows can be used to build viral genomic resources for pathogen surveillance in regions with high infectious disease burden.

microbiology↗

bioRxiv2026

Relatedness of Gardnerella prophages and their endolysins

The Gardnerella genus includes a complex sub-taxonomy of bacterial species and subgroups which have been implicated in bacterial vaginosis. We analyzed G. leopoldii, G. swidsinski, G. piotii, and G. vaginalis genomes available in public databases and predicted proviral sequences using Cenote-Taker3. We clustered 266 prophage sequences into 140 viral genera level groupings that encode four distinct gene clusters and 19 different lysin proteins. Analysis of the bacterial and prophage sequence phylogenies reveals that while there were no specific prophage sequence lineages that infected each bacterial host, there is clustering of the prophage sequences by bacterial species within the Gardnerella genus.

microbiology↗

bioRxiv2026

Atypical myxomatosis in European rabbits is caused by the recombinant myxoma virus involved in species jumping into hares

Myxoma virus (MYXV), a member of the Leporipoxvirus genus (species Leporipoxvirus myxoma; family Poxviridae), causes a highly lethal disease known as myxomatosis in European rabbits. In late 2018, a new natural MYXV isolate, MYXV-Tol (a.k.a. hare MYXV; ha-MYXV), emerged and caused myxomatosis-like disease with high mortality in Iberian hares, European brown hares, and European rabbits. This variant contains an approximately 2.8-kb insertion of a recombination cassette within the M009L gene encoding four additional genes, including the C7-like host range gene, M159L. M159 is essential for replication of MYXV-Tol in hare cells and is likely a key determinant of its pathogenicity in both hares and rabbits. Here, we compared the pathogenicity of wild-type MYXV-Tol (vMyx-Tol), an M159 deletion strain (vMyx-Tol-M159KO), and the classical MYXV-Lau strain (vMyx-Lau) in European rabbits. All three viruses caused systemic disease; however, vMyx-Tol and vMyx-Tol-M159KO produced clinical signs distinct from classical myxomatosis. Infection with vMyx-Tol and vMyx-Tol-M159KO was characterized by the absence of the typical primary and secondary nodular lesions, and caused severe edema, marked fluid accumulation, lymphocyte infection, and significantly reduced or no virus-neutralizing antibody responses. The disease caused by both vMyx-Tol and vMyx-Tol-M159KO progressed rapidly within 9-11 days, resulting in animals reaching humane euthanasia endpoints like vMyx-Lau. Deletion of M159 did not significantly alter MYXV-Tol pathogenicity in rabbits. Collectively, these findings demonstrate that MYXV-Tol has evolved to cause an atypical, amyxomatous-like acute to hyperacute disease in European rabbits and likely in hares. SignificanceNatural evolution enables viruses to cross species barriers and adapt to new hosts. Myxoma virus (MYXV), released in the 1950s in Australia and Europe as a biocontrol agent against European rabbits, became a classic model for real-time monitoring of virus evolution, virulence, and host adaptation. Although MYXV is typically host-restricted, a newly emerged natural isolate, MYXV-Tol, causes lethal disease in both hares and rabbits. Here, we show that MYXV-Tol induces an atypical, amyxomatous-like disease characterized by the absence of nodular lesions, severe edema, lymphocyte infection, and markedly reduced virus-neutralizing antibody responses. These findings reveal previously unrecognized virus-host interactions that shape disease outcome and provide new insight into the mechanisms driving viral adaptation and evolution.

microbiology↗

bioRxiv2026

Skuas as sentinels of high pathogenicity avian influenza H5N1 on the Antarctic Peninsula in the 2024/2025 austral summer

Despite Antarcticas geographic isolation, the first incursion of high pathogenicity avian influenza (HPAI) H5N1 was detected in the 2023/24 austral summer. Surveillance for HPAI H5N1 in Antarctica remains patchy due to logistical, financial, and infrastructure challenges, with many suspected cases remaining unconfirmed, and few viral genomes sequences available to date. Through the 2024/25 austral summer we undertook five sampling expeditions to the South Shetland Islands and Antarctic Peninsula facilitated by cruise ships/operators. Across more than 500 faecal environmental samples collected from apparently healthy penguins and marine mammals, we found no detectable evidence of HPAI H5N1. However, HPAI H5N1 was detected in all but one of the skua carcasses sampled, which, in most cases, were found within meters of penguin sub-colonies. All HPAI H5N1 viral genomes sequences from skuas on the Antarctic Peninsula fell within a single lineage, which included those genomes from skuas sampled in the 2024/25 season from the South Shetland Islands. Genomes were in a different clade to those from the Antarctic Peninsula collected in the 2023/24 austral summer. Our results confirm although the prevalence may be low, HPAI H5N1 is established in Antarctica, emphasizing the need for ongoing surveillance to monitor and mitigate threats to wildlife, even in the planets most isolated regions.

microbiology↗

bioRxiv2024

Widespread Horizontal Gene Transfer Among Animal Viruses

The initial objective of this study was to shed light on the evolution of small DNA tumor viruses by analyzing de novo assemblies of publicly available deep sequencing datasets. The survey generated a searchable database of contig snapshots representing more than 100,000 Sequence Read Archive records. Using modern structure-aware search tools, we iteratively broadened the search to include an increasingly wide range of other virus families. The analysis revealed a surprisingly diverse range of chimeras involving different virus groups. In some instances, genes resembling known DNA-replication modules or known virion protein operons were paired with unrecognizable sequences that structural predictions suggest may represent previously unknown replicases and novel virion architectures. Discrete clades of an emerging group called adintoviruses were discovered in datasets representing humans and other primates. As a proof of concept, we show that the contig database is also useful for discovering RNA viruses and candidate archaeal phages. The ancillary searches revealed additional examples of chimerization between different virus groups. The observations support a gene-centric taxonomic framework that should be useful for future virus-hunting efforts.

microbiology↗

bioRxiv2023

No evidence for highly pathogenic avian influenza virus H5N1 (clade 2.3.4.4b) in the Antarctic region during the austral summer 2022/23

The current highly pathogenic avian influenza H5N1 panzootic has substantial impacts on wild birds and marine mammals. Although major outbreaks occurred in South America, incursion to Antarctica emerged late in the breeding season of 2023/2024 and was confined the wider region of the Antarctic Peninsula. To infer potential underlying processes, we compiled H5N1 surveillance from Antarctica and Sub-Antarctic Islands prior to the first confirmed cases.

microbiology↗

bioRxiv2023

Population ecology and potential biogeochemical impacts of ssDNA and dsDNA soil viruses along a permafrost thaw gradient

Climate change is disproportionately warming northern peatlands, which may release large carbon stores via increased microbial activity. While there are many unknowns about such microbial responses, virus roles are especially poorly characterized with studies to date largely restricted to "bycatch" from bulk metagenomes. Here, we used optimized viral particle purification techniques on 20 samples along a highly contextualized peatland permafrost thaw gradient, extracted and sequenced viral particle DNA using two library kits to capture single-stranded (ssDNA) and double-stranded (dsDNA) virus genomes (40 total viromes), and explored their diversity and potential ecosystem impacts. Both kits recovered similar dsDNA virus numbers, but only one also captured thousands of ssDNA viruses. Combining these data, we explored population-level ecology using genomic representation from 9,560 viral operational taxonomic units (vOTUs); nearly a 4-fold expansion from permafrost-associated soils, and 97% of which were novel when compared against large datasets from soils, oceans, and the human gut. In silico predictions identified putative hosts for 44% (4,149 dsDNA + 17 ssDNA) of the identified vOTUs spanning 2 eukaryotic, 12 archaeal, and 30 bacterial phyla. The recovered vOTUs encoded 1,684 putative auxiliary metabolic genes (AMGs) and other metabolic genes carried by [~]10% of detected vOTUs, of which 46% were related to carbon processing and 644 were novel. These AMGs grouped into five functional categories and 11 subcategories, and nearly half (47%) of the AMGs were involved in carbon utilization. Of these, 112 vOTUs encoded 123 glycoside hydrolases spanning 15 types involved in the degradation of polysaccharides (e.g., cellulose) to monosaccharides (e.g., galactose), or further monosaccharide degradation, which suggests virus involvement in myriad metabolisms including fermentation and central carbon metabolism. These findings expand the scope of viral roles in microbial carbon processing and suggest viruses may be critical for understanding the fate of soil organic carbon in peatlands.

microbiology↗

bioRxiv2022

African army ants at the forefront of virome surveillance in a remote tropical forest

In this study, we used a predator-enabled metagenomics strategy to sample the virome of a remote and difficult-to-access densely forested African tropical region. Specifically, we focused our study on the use of army ants of the genus Dorylus that are obligate collective foragers and group predators that attack and overwhelm a broad array of animal prey. Using 209 army ant samples collected from 29 colonies and the virion-associated nucleic acid-based metagenomics approach, we showed that a broad diversity of bacterial, plant, invertebrate and vertebrate viral sequences were accumulated by army ants: including sequences from 157 different viral genera in 56 viral families. This suggests that using predators and scavengers such as army ants to sample broad swathes of tropical forest viromes can shed light on the composition and the structure of viral populations of these complex and inaccessible ecosystems.

microbiology↗

bioRxiv2022

Treatment with anti-inflammatory viral serpin modulates immuno-thrombotic responses and improves outcomes in SARS-CoV-2 infected mice

1.Severe acute respiratory distress syndrome (ARDS) during SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2) infection, manifests as uncontrolled lung inflammation and systemic thrombosis with high mortality. Anti-viral drugs and monoclonal antibodies can reduce COVID-19 severity if administered in the early viremic phase, but treatments for later stage immuno-thrombotic syndrome and long COVID are limited. Serine protease inhibitors (SERPINS) regulate activated proteases during thrombotic, thrombolytic and immune responses. The myxoma poxvirus-derived Serp-1 protein is a secreted immunomodulatory serpin that targets activated coagulation and complement protease pathways as part of a self-defense strategy to combat viral clearance by the innate immune system. When purified and utilized as an anti-immune therapeutic, Serp-1 is effective as an anti-inflammatory drug in multiple animal models of inflammatory lung disease and vasculitis. Here, we describe systemic treatment with purified PEGylated Serp-1 (PEGSerp-1) as a therapy for immuno-thrombotic complications during ARDS. Treatment with PEGSerp-1 in two distinct mouse-adapted SARS-CoV-2 models in C57Bl/6 and BALB/c mice reduced lung and heart inflammation, with improved clinical outcomes. PEGSerp-1 significantly reduced M1 macrophage invasion in the lung and heart by modifying urokinase-type plasminogen activator receptor (uPAR) and complement membrane attack complex (MAC). Sequential changes in urokinase-type plasminogen activator receptor (uPAR) and serpin gene expression were observed in lung and heart with PEGSerp-1 treatment. PEGSerp-1 is a highly effective immune-modulator with therapeutic potential for treatment of severe viral ARDS with additional potential to reduce late SARS-CoV-2 complications related to immune-thrombotic events that persist during long COVID. SignificanceSevere acute respiratory distress syndrome (ARDS) in SARS-CoV-2 infection manifests as uncontrolled tissue inflammation and systemic thrombosis with high mortality. Anti-viral drugs and monoclonal antibodies reduce COVID-19 severity if administered early, but treatments for later stage immuno-thrombosis are limited. Serine protease inhibitors (SERPINS) regulate thrombotic, thrombolytic and complement pathways. We investigate here systemic treatment with purified poxvirus-derived PEGSerp-1 as a therapeutic for immuno-thrombotic complications in viral ARDS. PEGSerp-1 treatment in two mouse-adapted SARS-CoV-2 models (C57Bl/6 and BALB/c) significantly reduced lung and heart inflammation and improved clinical outcomes, with sequential changes in thrombolytic (uPAR) and complement expression. PEGSerp-1 is a highly effective immune-modulator with therapeutic potential for immune-thrombotic complications in severe viral ARDS and has potential benefit for long COVID.

microbiology↗

bioRxiv2021

A novel lineage of polyomaviruses identified in bark scorpions

Polyomaviruses are non-enveloped viruses with circular double-stranded DNA genomes that range in size from [~]4-7 kilobasepairs. Initially identified in mammals, polyomaviruses have now been identified in birds and a few fish species. Although fragmentary polyomavirus-like sequences have been detected as apparent hitchhikers in shotgun genomics datasets for various arthropods, the possible diversity of these viruses in invertebrates remains unclear. In general, polyomaviruses are host-specific, showing strong evidence of host-virus co-evolution. Identification of polyomaviruses in a broader range of animals could shed useful light on the evolutionary history of this medically important group of viruses. Scorpions are predatory arachnids that are among the oldest terrestrial animals. Thus far, viromes of arachnids have been under-sampled and understudied. Here, high-throughput sequencing and traditional molecular techniques were used to explore the diversity of circular DNA viruses associated with bark scorpions (Centruroides sculpturatus) from the greater Phoenix area, Arizona, USA. The complete genomes of eight novel polyomaviruses were identified. Analysis of Centruroides transcriptomic datasets elucidated the splicing of the viral late gene array, which is more complex than that of vertebrate polyomaviruses. Phylogenetic analysis provides further evidence of co-divergence of polyomaviruses with their hosts, suggesting that at least one ancestral species of polyomaviruses was circulating amongst the primitive common ancestors of arthropods and chordates.

microbiology↗

bioRxiv2021

Co-evolutionary analysis suggests a role for TLR9 in papillomavirus restriction

A.Upon infection, DNA viruses can be sensed by pattern recognition receptors (PRRs) leading to the activation of type I and III interferons, aimed at blocking infection. Therefore, viruses must inhibit these signaling pathways, avoid being detected, or both. Papillomavirus virions are trafficked from early endosomes to the Golgi apparatus and wait for the onset of mitosis to complete nuclear entry. This unique subcellular trafficking strategy avoids detection by cytoplasmic PRRs, a property that may contribute to establishment of infection. However, as the capsid uncoats within acidic endosomal compartments, the viral DNA may be exposed to detection by toll-like receptor (TLR) 9. In this study we characterize two new papillomaviruses from bats and use molecular archeology to demonstrate that their genomes altered their nucleotide composition to avoid detection by TLR9, providing evidence that TLR9 acts as a PRR during papillomavirus infection. Furthermore, we demonstrate that TLR9, like other components of the innate immune system, is under evolutionary selection in bats, providing the first direct evidence for co-evolution between papillomaviruses and their hosts.

microbiology↗

bioRxiv2021

Genomic Skimming and Nanopore Sequencing Uncover Cryptic Hybridization in One of World's Most Threatened Primates

The Brazilian buffy-tufted-ear marmoset (Callithrix aurita), one of the worlds most endangered primates, is threatened by anthropogenic hybridization with exotic, invasive marmoset species. As there are few genetic data available for C. aurita, we developed a PCR-free protocol with minimal technical requirements to rapidly generate genomic data with genomic skimming and portable nanopore sequencing. With this direct DNA sequencing approach, we successfully determined the complete mitogenome of a marmoset that we initially identified as C. aurita. The obtained nanopore-assembled sequence was highly concordant with a Sanger sequenced version of the same mitogenome. Phylogenetic analyses unexpectedly revealed that our specimen was a cryptic hybrid, with a C. aurita phenotype and C. penicillata mitogenome lineage. We also used publicly available mitogenome data to determine diversity estimates for C. aurita and three other marmoset species. Mitogenomics holds great potential to address deficiencies in genomic data for endangered, non-model species such as C. aurita. However, we discuss why mitogenomic approaches should be used in conjunction with other data for marmoset species identification. Finally, we discuss the utility and implications of our results and genomic skimming/nanopore approach for conservation and evolutionary studies of C. aurita and other marmosets.

evolutionary biology↗

bioRxiv2021

Predicting the zoonotic capacity of mammal species for SARS-CoV-2

Back and forth transmission of SARS-CoV-2 between humans and animals may lead to wild reservoirs of virus that can endanger efforts toward long-term control of COVID-19 in people, and protecting vulnerable animal populations that are particularly susceptible to lethal disease. Predicting high risk host species is key to targeting field surveillance and lab experiments that validate host zoonotic potential. A major bottleneck to predicting animal hosts is the small number of species with available molecular information about the structure of ACE2, a key cellular receptor required for viral cell entry. We overcome this bottleneck by combining species ecological and biological traits with 3D modeling of virus and host cell protein interactions using machine learning methods. This approach enables predictions about the zoonotic capacity of SARS-CoV-2 for over 5,000 mammals -- an order of magnitude more species than previously possible. The high accuracy predictions achieved by this approach are strongly corroborated by in vivo empirical studies. We identify numerous common mammal species whose predicted zoonotic capacity and close proximity to humans may further enhance the risk of spillover and spillback transmission of SARS-CoV-2. Our results reveal high priority areas of geographic overlap between global COVID-19 hotspots and potential new mammal hosts of SARS-CoV-2. With molecular sequence data available for only a small fraction of potential host species, predictive modeling integrating data across multiple biological scales offers a conceptual advance that may expand our predictive capacity for zoonotic viruses with similarly unknown and potentially broad host ranges.

ecology↗

bioRxiv2020

VIRIDIC - a novel tool to calculate the intergenomic similarities of prokaryote-infecting viruses

Nucleotide based intergenomic similarities are useful to understand how viruses are related with each other and to classify them. Here we have developed VIRIDIC, which implements the traditional algorithm used by the International Committee on Taxonomy of Viruses (ICTV), Bacterial and Archaeal Viruses Subcommittee, to calculate virus intergenomic similarities. When compared with other software, VIRIDIC gave the best agreement with the traditional algorithm. Furthermore, it proved best at estimating the relatedness between more distantly related phages, relatedness that other tools can significantly overestimate. In addition to the intergenomic similarities, VIRIDIC also calculates three indicators of the alignment ability to capture the relatedness between viruses: the aligned fractions for each genome in a pair and the length ratio between the two genomes. The main output of VIRIDIC is a heatmap integrating the intergenomic similarity values with information regarding the genome lengths and the aligned genome fraction. VIRIDIC is available at viridic.icbm.de, both as a web-service and a stand-alone tool. It allows fast analysis of large phage genome datasets, especially in the stand-alone version, which can be run on the user’s own servers and can be integrated in bioinformatics pipelines. VIRIDIC was developed having viruses of Bacteria and Archaea in mind, however, it could potentially be used for eukaryotic viruses as well, as long as they are monopartite.Competing Interest StatementThe authors have declared no competing interest.View Full Text

microbiology↗

bioRxiv2020

Unveiling Crucivirus Diversity by Mining Metagenomic Data

The discovery of cruciviruses revealed the most explicit example of a common protein homologue between DNA and RNA viruses to date. Cruciviruses are a novel group of circular Rep-encoding ssDNA (CRESS-DNA) viruses that encode capsid proteins (CPs) that are most closely related to those encoded by RNA viruses in the family Tombusviridae. The apparent chimeric nature of the two core proteins encoded by crucivirus genomes suggests horizontal gene transfer of CP genes between DNA and RNA viruses. Here, we identified and characterized 451 new crucivirus genomes and ten CP-encoding circular genetic elements through de novo assembly and mining of metagenomic data. These genomes are highly diverse, as demonstrated by sequence comparisons and phylogenetic analysis of subsets of the protein sequences they encode. Most of the variation is reflected in the replication associated protein (Rep) sequences, and much of the sequence diversity appears to be due to recombination. Our results suggest that recombination tends to occur more frequently among groups of cruciviruses with relatively similar capsid proteins, and that the exchange of Rep protein domains between cruciviruses is rarer than gene exchange. Altogether, we provide a comprehensive and descriptive characterization of cruciviruses. IMPORTANCEViruses are the most abundant biological entities on Earth. In addition to their impact on animal and plant health, viruses have important roles in ecosystem dynamics as well as in the evolution of the biosphere. Circular Rep-encoding single-stranded (CRESS) DNA viruses are ubiquitous in nature, many are agriculturally important, and are viruses that appear to have multiple origins from prokaryotic plasmids. CRESS-DNA viruses such as the cruciviruses, have homologues of capsid proteins (CPs) encoded by RNA viruses. The genetic structure of cruciviruses attests to the transfer of capsid genes between disparate groups of viruses. However, the evolutionary history of cruciviruses is still unclear. By collecting and analyzing cruciviral sequence data, we provide a deeper insight into the evolutionary intricacies of cruciviruses. Our results reveal an unexpected diversity of this virus group, with frequent recombination as an important determinant of variability.

evolutionary biology↗

bioRxiv2019

Genetic characterization of a recombinant myxoma virus leap into the Iberian hare (Lepus granatensis)

Myxomatosis is a lethal disease of wild European and domestic rabbits (Oryctolagus cuniculus) caused by a Myxoma virus (MYXV) infection, a leporipoxvirus that is found naturally in some Sylvilagus rabbit species in South America and California. The introduction of MYXV in the early 1950s into feral European rabbit populations in Australia and Europe demonstrate the best documented field example of host-virus coevolution following a cross-species transmission. Recently, a new cross-species jump of MYXV has been suggested in both Great Britain and Spain, where European brown hares (Lepus europaeus) and Iberian hares (Lepus granatensis) were found dead with lesions consistent with those observed in myxomatosis. To investigate the possibility of a new cross-species transmission event by MYXV, tissue samples collected from a wild Iberian hare found dead in Spain (Toledo region) were analyzed and deep sequenced. Our results report a new MYXV strain (MYXV Toledo) in the tissues of this species. The genome of this new strain encodes three disrupted genes (M009L, M036L and M152R) and a novel 2.8 KB recombinant region that resulted from an insertion of four novel poxviral genes towards the 5 end of its genome. From the open reading frames inserted into the MYXV Toledo strain, a new orthologue of a poxvirus host range gene family member was identified which is related to the MYXV gene M064R. Overall, we confirmed the identity of a new MYXV strain in Iberian hares that we hypothesize was able to more effectively counteract the host defenses in hares and start an infectious process in this new host.

microbiology↗

bioRxiv2019

crAssphage abundance and genomic selective pressure correlate with altered bacterial abundance in the fecal microbiota of South African mother-infant dyads

crAssphages are a class of bacteriophages that are highly abundant in the human gastrointestinal tract. Accordingly, crAssphage genomes have been identified in most human fecal viral metagenome studies. However, we currently have an incomplete understanding of factors impacting the transmission frequencies of these phages between mothers and infants, and the evolutionary pressures associated with such transmissions. Here, we use metagenome sequencing of stool-associated virus-like particles to identify the prevalence of crAssphage across ten South African mother-infant dyads that are discordant for HIV infection. We report the identification of a complete 97kb crAssphage genome, parts of which are detected at variable levels across each mother-infant dyad. We observed average nucleotide sequence identities of >99% for crAssphages from related mother-infant pairs but [~]97% identities between crAssphages from unrelated mothers and infants: a finding strongly suggestive of vertical mother to infant transmission. We further analyzed patterns of nucleotide diversity across the crAssphage sequences described here, identifying particularly elevated positive selection in RNA polymerase and phage tail protein encoding genes, which we validated against a crAssphage genome from previous studies. Using 16S rRNA gene sequencing, we found that the relative abundances of Bacteroides thetaiotaomicron and Parabacteroides merdae (Order: Bacteroidales) were differentially correlated with crAssphage abundance. Together, our results reveal that crAssphages may be vertically transmitted from mothers to their infants and that hotspots of selection within crAssphage RNA polymerase and phage tail protein encoding genes are potentially mediated by interactions between crAssphages and their bacterial partners.\n\nImportancecrAssphages are an ubiquitous member of the human gut microbiome and modulate interactions with key bacterial associates within the order Bacteroidales. However, the role of this interaction in the genomic evolution of crAssphage remains unclear. Across a longitudinally sampled cohort of ten South African mother-infant dyads, we use metagenome sequencing of the fecal virome and 16S rRNA gene sequencing of the fecal bacterial microbiota to elucidate the ecological and evolutionary dynamics of these interactions. Here, we demonstrate elevated levels of crAssphage average nucleotide identity between related mother-infant dyads as compared to unrelated individuals, suggesting vertical transmission. We report strong positive selection in crAssphage RNA polymerase and phage tail protein genes. Finally, we demonstrate that crAssphage abundance is linearly correlated (P < 0.014) with the abundance of two bacterial taxa, Bacteroides thetaiotaomicron and Parabacteroides merdae. These results suggest that phage-bacterial interactions may help shape ecological and evolutionary dynamics in the gut.

microbiology↗

bioRxiv2019

Discovery of several thousand highly diverse circular DNA viruses

Although it is suspected that there are millions of distinct viral species, fewer than 9,000 are catalogued in GenBanks RefSeq database. We selectively enriched for and amplified the genomes of circular DNA viruses in over 70 animal samples, ranging from cultured soil nematodes to human tissue specimens. A bioinformatics pipeline, Cenote-Taker, was developed to automatically annotate over 2,500 circular genomes in a GenBank-compliant format. The new genomes belong to dozens of established and emerging viral families. Some appear to be the result of previously undescribed recombination events between ssDNA viruses and ssRNA viruses. In addition, hundreds of circular DNA elements that do not encode any discernable similarities to previously characterized sequences were identified. To characterize these "dark matter" sequences, we used an artificial neural network to identify candidate viral capsid proteins, several of which formed virus-like particles when expressed in culture. These data further the understanding of viral sequence diversity and allow for high throughput documentation of the virosphere.

microbiology↗