Microviridae Goes Temperate: Microvirus-Related Proviruses Reside in the Genomes of Bacteroidetes

The Microviridae comprises icosahedral lytic viruses with circular single-stranded DNA genomes. The family is divided into two distinct groups based on genome characteristics and virion structure. Viruses infecting enterobacteria belong to the genus Microvirus, whereas those infecting obligate parasitic bacteria, such as Chlamydia, Spiroplasma and Bdellovibrio, are classified into a subfamily, the Gokushovirinae. Recent metagenomic studies suggest that members of the Microviridae might also play an important role in marine environments. In this study we present the identification and characterization of Microviridae-related prophages integrated in the genomes of species of the Bacteroidetes, a phylum not previously known to be associated with microviruses. Searches against metagenomic databases revealed the presence of highly similar sequences in the human gut. This is the first report indicating that viruses of the Microviridae lysogenize their hosts. Absence of associated integrase-coding genes and apparent recombination with dif-like sequences suggests that Bacteroidetes-associated microviruses are likely to rely on the cellular chromosome dimer resolution machinery. Phylogenetic analysis of the putative major capsid proteins places the identified proviruses into a group separate from the previously characterized microviruses and gokushoviruses, suggesting that the genetic diversity and host range of bacteriophages in the family Microviridae is wider than currently appreciated

Ratification vote on taxonomic proposals to the International Committee on Taxonomy of Viruses (2016)

This article lists the changes to virus taxonomy approved and ratified by the International Committee on Taxonomy of Viruses (ICTV) in April 2016. Changes to virus taxonomy (the Universal Scheme of Virus Classification of the International Committee on Taxonomy of Viruses [ICTV]) now take place annually and are the result of a multi-stage process. In accordance with the ICTV Statutes (http://​www.​ictvonline.​org/​statutes.​asp), proposals submitted to the ICTV Executive Committee (EC) undergo a review process that involves input from the ICTV Study Groups (SGs) and Subcommittees (SCs), other interested virologists, and the EC. After final approval by the EC, proposals are then presented for ratification to the full ICTV membership by publication on an ICTV web site (http://​www.​ictvonline.​org/​) followed by an electronic vote. The latest set of proposals approved by the EC was made available on the ICTV website by January 2016 (https://​talk.​ictvonline.​org/​files/​proposals/​). A list of these proposals was then emailed on 28 March 2016 to the 148 members of ICTV, namely the EC Members, Life Members, ICTV Subcommittee Members (including the SG chairs) and ICTV National Representatives. Members were then requested to vote on whether to ratify the taxonomic proposals (voting closed on 29 April 2016)

Novel haloarchaeal viruses from Lake Retba infecting Haloferax and Halorubrum species

The diversity of archaeal viruses is severely undersampled compared with that of viruses infecting bacteria and eukaryotes, limiting our understanding on their evolution and environmental impacts. Here, we describe the isolation and characterization of four new viruses infecting halophilic archaea from the saline Lake Retba, located close to Dakar on the coast of Senegal. Three of the viruses, HRPV10, HRPV11 and HRPV12, have enveloped pleomorphic virions and should belong to the family Pleolipoviridae, whereas the forth virus, HFTV1, has an icosahedral capsid and a long non-contractile tail, typical of bacterial and archaeal members of the order Caudovirales. Comparative genomic and phylogenomic analyses place HRPV10, HRPV11 and HRPV12 into the genus Betapleolipovirus, whereas HFTV1 appears to be most closely related to the unclassified Halorubrum virus HRTV-4. Differently from HRTV-4, HFTV1 encodes host-derived minichromosome maintenance helicase and PCNA homologues, which are likely to orchestrate its genome replication. HFTV1, the first archaeal virus isolated on a Haloferax strain, could also infect Halorubrum sp., albeit with an eightfold lower efficiency, whereas pleolipoviruses nearly exclusively infected autochthonous Halorubrum strains. Mapping of the metagenomic sequences from this environment to the genomes of isolated haloarchaeal viruses showed that these known viruses are underrepresented in the available viromes.Peer reviewe

Taxonomic assignment of uncultivated prokaryotic virus genomes is enabled by gene-sharing networks

© 2019, The Author(s), under exclusive licence to Springer Nature America, Inc. Microbiomes from every environment contain a myriad of uncultivated archaeal and bacterial viruses, but studying these viruses is hampered by the lack of a universal, scalable taxonomic framework. We present vConTACT v.2.0, a network-based application utilizing whole genome gene-sharing profiles for virus taxonomy that integrates distance-based hierarchical clustering and confidence scores for all taxonomic predictions. We report near-identical (96%) replication of existing genus-level viral taxonomy assignments from the International Committee on Taxonomy of Viruses for National Center for Biotechnology Information virus RefSeq. Application of vConTACT v.2.0 to 1,364 previously unclassified viruses deposited in virus RefSeq as reference genomes produced automatic, high-confidence genus assignments for 820 of the 1,364. We applied vConTACT v.2.0 to analyze 15,280 Global Ocean Virome genome fragments and were able to provide taxonomic assignments for 31% of these data, which shows that our algorithm is scalable to very large metagenomic datasets. Our taxonomy tool can be automated and applied to metagenomes from any environment for virus classification