# ICTV Virus Taxonomy Profile: Tosoviridae 2023

Yuri I Wolf, Mart Krupovic, Jens H Kuhn, Eugene V Koonin

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Yuri I Wolf, Mart Krupovic, Jens H Kuhn, Eugene V Koonin. ICTV Virus Taxonomy Profile: Tosoviridae 2023. Journal of General Virology, 2023, 104 (10), pp.001908. 10.1099/jgv.0.001908. pasteur-04313775

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# ICTV Virus Taxonomy Profile: *Tosoviridae* 2023

Yuri I. Wolf¹, Mart Krupovic², Jens H. Kuhn³ and Eugene V. Koonin¹,*

## Abstract

*Tosoviridae* is a family of negative-sense RNA viruses with genomes totaling about 12.3 kb that have been found in turtles. The tosovirid genome consists of two segments, each with two open reading frames (ORFs) in ambisense orientation. The small (S) segment encodes a nucleoprotein (NP) and a glycoprotein precursor (GPC); the large (L) segment encodes an L protein containing an RNA-directed RNA polymerase (RdRP) domain and a zinc-binding (Z) protein. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family *Tosoviridae*, which is available at *ictv.global/report/tosoviridae*.

<table><caption>**Table 1.** Characteristics of members of the family *Tosoviridae*</caption><thead><tr><th>Example</th><th>turtle fraservirus 1 (S segment: MZ458542; L segment: MZ458543), species Fraservirus testudinis, genus Fraservirus</th></tr></thead><tbody><tr><td>Virion</td><td>Enveloped, round or slightly oval; 110–125 nm</td></tr><tr><td>Genome</td><td>About 12.3 kb of bisegmented negative-sense RNA</td></tr><tr><td>Replication</td><td>Unknown</td></tr><tr><td>Translation</td><td>Unknown</td></tr><tr><td>Host range</td><td>Emydid and trionychid turtles</td></tr><tr><td>Taxonomy</td><td>Realm Riboviria, kingdom Orthornavirae, phylum Negarnaviricota; the family includes the genus Fraservirus and one species.</td></tr></tbody></table>

## VIRION

Tosovirids produce enveloped round or slightly oval particles 110–125 nm in diameter [1, 2] (Table 1).

## GENOME

The tosovirid genome comprises two segments (S and L) of linear negative-sense RNA with a total length of about 12.3 kb (S segment: about 5.7 kb; L segment: 6.6 kb). Each segment contains two ORFs in ambisense orientation (Fig. 1). The S segment encodes an NP and a GPC; the L segment encodes an L protein with an RdRP domain, and a Z protein

[1]. Superficially, this organization is reminiscent of that of arenavirid genomes [3].

## REPLICATION

Unknown.

## PATHOGENICITY

Turtle fraservirus 1 is highly virulent in emydid and trionychid turtles [1].

Received 04 October 2023; Accepted 06 October 2023; Published 24 October 2023

**Author affiliations:** ¹National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA; ²Institut Pasteur, Université Paris Cité, Archaeal Virology Unit, Paris 75015, France; ³Integrated Research Facility at Fort Detrick, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Fort Detrick, Frederick, MD 21702, USA.

*Correspondence: Eugene V. Koonin, koonin@ncbi.nlm.nih.gov

Keywords: ICTV Report; Taxonomy; *Tosoviridae*; fraservirus; turtle fraservirus 1.

Abbreviations: GPC, glycoprotein precursor; L, large; NP, nucleoprotein; RdRP, RNA-directed RNA polymerase; S, small; Z, zinc-binding. 001908

<figure><img src="image_3.png" /></figure>
<figure><img src="image_4.png" /><figcaption>**Fig. 1.** Genome organisation of turtle fraservirus 1. ORFs are coloured according to the predicted protein function (GP, glycoprotein precursor gene; NP, nucleoprotein gene; L, large protein gene encoding an RNA-directed RNA polymerase [RdRP] domain; Z, zinc-binding protein gene).</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Phylogenetic relationships of turtle fraservirus 1. A phylogenetic tree was reconstructed for an alignment of consensus sequences of the RdRP core domains of the ICTV Virus Metadata Resource (VMR) set of *Negarnaviricota* [5] using the FastTree programme. Branches are collapsed to order level. For full details see *Tosoviridae* ICTV Report.</figcaption></figure>

## TAXONOMY

Current taxonomy: **ictv.global/taxonomy**. The family *Tosoviridae* includes the genus *Fraservirus* and the species *Fraservirus testudinis* for viruses that infect turtles. Tosovirids are most closely related to, but distinct from, viruses in the subphyla *Haploviricotina* and *Polyploviricotina* [1, 4] (Fig. 2).

## References

1. Waltzek TB, Stacy BA, Ossiboff RJ, Stacy NI, Fraser WA, et al. A novel group of negative-sense RNA viruses associated with epizootics in managed and free-ranging freshwater turtles in Florida, USA. *PLoS Pathog* 2022;18:e1010258.

2. Grimwood RM, Fortune-Kelly G, Holmes EC, Ingram T, Geoghegan JL. Host specificity shapes fish viromes across lakes on an isolated remote island. *bioRxiv* 2023;587:109884.

## RESOURCES

Full ICTV Report on the family *Tosoviridae*: www.ictv.global/report/tosoviridae

### Funding information

Production of this Profile, the ICTV Report, and associated resources was supported by the Microbiology Society. This work was supported in part through the Laulima Government Solutions, LLC, prime contract with the U.S. National Institute of Allergy and Infectious Diseases (NIAID), under Contract No. HHSN272201800013C. J.H.K. performed this work as an employee of Tunnell Government Services (TGS), a subcontractor of Laulima Government Solutions, LLC, under Contract No. HHSN272201800013C. The content of this publication should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Health and Human Services or of the institutions and companies affiliated with the authors, nor does mention of trade names, commercial products, or organisations imply endorsement by the U.S. Government.

### Acknowledgements

We thank Stuart G. Siddell, Elliot J. Lefkowitz, Sead Sabanadzovic, Peter Simmonds, F. Murilo Zerbini, Evelien Adriaenssens, Luisa Rubino, Arvind Varsani (ICTV Report Editors), and Donald B. Smith (Managing Editor, ICTV Report). We thank Anya Crane (Integrated Research Facility at Fort Detrick, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Fort Detrick, Frederick, MD, USA) for critically editing the manuscript.

### Conflicts of interest

The authors declare that there are no conflicts of interest.

3. Radoshitzky SR, Buchmeier MJ, Charrel RN, Gonzalez J-P, Günther S, et al. ICTV virus taxonomy profile: *Arenaviridae* 2023. *J Gen Virol* 2023;104:e001891.

4. Kuhn JH, Abe J, Adkins S, Alkhovsky SV, Avšič-Županc T, et al. Annual (2023) Taxonomic update of RNA-directed RNA polymerase-encoding negative-sense RNA viruses (realm *Riboviria*: kingdom *Orthornavirae*: phylum *Negarnaviricota*). *J Gen Virol* 2023;104:e001864.

5. Neri U, Wolf YI, Roux S, Camargo AP, Lee B, et al. Expansion of the global RNA virome reveals diverse clades of bacteriophages. *Cell* 2022;185:4023–4037.