# ICTV Virus Taxonomy Profile: Adnaviria 2025

Mart Krupovic, Fengbin Wang, Virginija Cvirkaite-Krupovic, Jens H Kuhn, Valerian V Dolja, David Prangishvili, Edward H Egelman, Eugene V Koonin

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► To cite this version:

Mart Krupovic, Fengbin Wang, Virginija Cvirkaite-Krupovic, Jens H Kuhn, Valerian V Dolja, et al. ICTV Virus Taxonomy Profile: Adnaviria 2025. Journal of General Virology, 2025, 106 (3), pp.002091. 10.1099/jgv.0.002091. pasteur-05121251

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# ICTV Virus Taxonomy Profile: Adnaviria 2025

Mart Krupovic¹*, Fengbin Wang², Virginija Cvirkaite-Krupovic¹, Jens H. Kuhn³, Valerian V. Dolja⁴, David Prangishvili¹,⁵, Edward H. Egelman⁶ and Eugene V. Koonin⁷

## Abstract

Viruses assigned to the realm *Adnaviria* have linear, dsDNA genomes in which the DNA is structured in the A-form rather than the usual B-form. Virions are flexible or rigid filaments, with or without envelopes. Adnavirians share homologous major capsid proteins (MCPs) with a distinct α-helical structural fold not observed in other known viruses. The MCPs form homodimeric or heterodimeric capsomers that wrap around and condense the genomic dsDNA into helically symmetrical virions. Adnavirians infect hyperthermophilic, thermoacidophilic and methanotrophic archaea. This is a summary of the International Committee on Taxonomy of Viruses Report on the realm *Adnaviria*, which is available at **ictv.global/report/adnaviria**.

<table><caption>**Table 1.** Characteristics of viruses of the realm *Adnaviria*</caption><tr><td>Example</td><td>Sulfolobus islandicus rod-shaped virus 2 (AJ344259), species Icerudivirus hveragerdiense</td></tr><tr><td>Virion</td><td>Flexible or rigid filaments, with or without envelopes, 20–38 nm diameter, 400–2,000 nm long with one or two α-helical MCPs</td></tr><tr><td>Genome</td><td>Linear dsDNA of 17.6–41.5 kb, the DNA being in the A-form</td></tr><tr><td>Replication</td><td>Variable</td></tr><tr><td>Translation</td><td>Host translation machinery</td></tr><tr><td>Host range</td><td>Primarily hyperthermophilic and thermoacidophilic archaea of the phylum Thermoproteota</td></tr><tr><td>Taxonomy</td><td>The realm includes at least 1 kingdom, 1 phylum, 1 class, 3 orders, 6 families, 15 genera and 33 species</td></tr></table>

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** MCPs of adnavirians. (a) Capsomers consist of MCP dimers (shown in blue and magenta). A homodimer of Saccharolobus solfataricus rod-shaped virus 1 (*Rudiviridae*) is shown as an example. (b) MCP dimers tightly wrap around the genomic A-form DNA (magenta).</figcaption></figure>

## VIRION

Virions of adnavirians are filamentous, either flexible with (e.g., *Lipothrixviridae*, *Ungulaviridae* and *Tristromaviridae*) or non-flexible without (e.g. *Rudiviridae*) an envelope (Table 1). Virions are 20–38 nm in diameter and 400–2,000 nm in length.

Adnavirians encode homologous major capsid proteins (MCPs) with a unique α-helical fold (Fig. 1). *Rudivirids* encode a single MCP, whereas other adnavirians encode two paralogous, structurally similar MCPs [1]. High-resolution structures are available for *rudivirids* [2, 3], *lipothrixvirids* [2, 4], *ungulavirids* [5].

Received 10 March 2025; Accepted 12 March 2025; Published 26 March 2025

**Author affiliations:** ¹Institut Pasteur, Université Paris Cité, CNRS UMR6047, Archaeal Virology Unit, 75015 Paris, France; ²Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35233, USA; ³Integrated Research Facility at Fort Detrick, Division of Clinical Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Fort Detrick, Frederick, MD 21702, USA; ⁴Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA; ⁵Ivane Javakhishvili Tbilisi State University, 0179 Tbilisi, Georgia; ⁶Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22903, USA; ⁷Computational Biology Branch, Division of Intramural Research, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.

*Correspondence: Mart Krupovic, mart.krupovic@pasteur.fr

Keywords: *Adnaviria*; ICTV Report; *Lipothrixviridae*; *Rudiviridae*; taxonomy; viruses of archaea.

Abbreviations: ICTV, International Committee on Taxonomy of Viruses; MCP, major capsid protein.

002091

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[5] and tristromavirids [6]. The capsomer, the principal building block of the capsid, is an MCP dimer, a homodimer in rudivirids and a heterodimer in other adnavirians. MCP dimers tightly wrap around genomic dsDNA, effectively leading to its dehydration (Fig. 1). In addition, positively-charged residues coordinate the phosphates such that the DNA in the virions exists in the A-form [2]. Extensive protein-protein and protein-DNA interactions result in the coiling and compaction of viral DNA into helically symmetric virions. The terminal structures capping the filamentous virions on both ends and implicated in host recognition are composed of minor structural proteins and are usually genus-specific. When present, envelopes contain host-derived lipids.

## GENOME

Adnavirians have linear dsDNA genomes of 17.6–41.5 kb that contain terminal inverted repeats. The two DNA strands can be covalently linked [7] or contain covalently attached terminal proteins [8]. Adnavirians do not share universal core genes other than those encoding the MCPs. However, most members encode diverse host takeover and counter-defence proteins.

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Taxonomy of the realm *Adnaviria*.</figcaption></figure>

## References

1. Baquero DP, Liu Y, Wang F, Egelman EH, Prangishvili D, et al. Structure and assembly of archaeal viruses. *Adv Virus Res* 2020;108:127–164.

2. Wang F, Baquero DP, Beltran LC, Su Z, Osinski T, et al. Structures of filamentous viruses infecting hyperthermophilic archaea explain DNA stabilization in extreme environments. *Proc Natl Acad Sci USA* 2020;117:19643–19652.

3. DiMaio F, Yu X, Rensen E, Krupovic M, Prangishvili D, et al. Virology. A virus that infects a hyperthermophile encapsidates A-form DNA. *Science* 2015;348:914–917.

4. Liu Y, Osinski T, Wang F, Krupovic M, Schouten S, et al. Structural conservation in a membrane-enveloped filamentous virus infecting a hyperthermophilic acidophile. *Nat Commun* 2018;9:3360.

5. Kasson P, DiMaio F, Yu X, Lucas-Staat S, Krupovic M, et al. Model for a novel membrane envelope in a filamentous hyperthermophilic virus. *Elife* 2017;6:e26268.

## REPLICATION

Rudivirids, tristromavirids and ungulavirids recognize their respective hosts by binding to extracellular filaments. Adnavirians use diverse genome replication strategies. Virion assembly and envelopment take place in the cytoplasm [9]. All characterized adnavirians are lytic viruses.

## TAXONOMY

Current taxonomy: **ictv.global/taxonomy**. The realm (Fig. 2) was established in 2021 [10]. Hosts are thermophilic archaea of the phylum *Thermoproteota*, specifically of orders *Sulfolobales* (rudivirids, lipothrixvirids and ungulavirids), *Thermoproteales* (tristromavirids) and *Candidatus* *Bathyarchaeales* (chiyouvirids), and methanotrophs of the class *Candidatus* *Syntropharchaeia* in phylum *Halobacteriota* (ahmunvirids).

## RESOURCES

Full ICTV Report on the realm *Adnaviria*: ictv.global/report/adnaviria.

### Funding information

Production of this Profile, the ICTV Report and associated resources was supported by the Microbiology Society.

### Acknowledgements

We thank Evelien Adriaenssens (Editor-in-Chief, ICTV Report), ICTV Report Editors and Donald B. Smith (Managing Editor, ICTV Report). We also thank Anya Crane (Integrated Research Facility at Fort Detrick, Division of Clinical Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Frederick, MD, USA) for critically editing the manuscript. This project was supported in part through a 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 views and conclusions contained in this document are those of the authors and 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.

### Conflicts of interest

The authors declare that there are no conflicts of interest.

6. Wang F, Baquero DP, Su Z, Osinski T, Prangishvili D, et al. Structure of a filamentous virus uncovers familial ties within the archaeal virosphere. *Virus Evol* 2020;6:veaa023.

7. Blum H, Zillig W, Mallok S, Domdey H, Prangishvili D. The genome of the archaeal virus SIRV1 has features in common with genomes of eukaryal viruses. *Virology* 2001;281:6–9.

8. Pina M, Basta T, Quax TEF, Joubert A, Baconnais S, et al. Unique genome replication mechanism of the archaeal virus AFV1. *Mol Microbiol* 2014;92:1313–1325.

9. Baquero DP, Gazi AD, Sachse M, Liu J, Schmitt C, et al. A filamentous archaeal virus is enveloped inside the cell and released through pyramidal portals. *Proc Natl Acad Sci USA* 2021;118:e2105540118.

10. Krupovic M, Kuhn JH, Wang F, Baquero DP, Dolja VV, et al. *Adnaviria*: a new realm for archaeal filamentous viruses with linear A-form double-stranded DNA genomes. *J Virol* 2021;95:e0067321.