Family: Globuloviridae

Since only one genus is currently recognized, the family description corresponds to the genus description.

Genus Globulovirus

Type species Pyrobaculum spherical virus

Virion properties

Morphology

Virions are spherical, 70–100 nm in diameter, with spherical protrusions, about 15 nm in diameter (Figure 1a). Virions carry a lipid-containing envelope. It encases a superhelical core, consisting of linear dsDNA and nucleoproteins (Figure 1b).

Physicochemical and physical properties

Virion buoyant density in sucrose is about 1.3 g cm⁻³. Virions are highly heat-stable. Prolonged exposure to oxygen does not affect the efficiency of infection of the strictly anaerobic hosts.

Nucleic acid

Virion contains a single molecule of linear dsDNA, comprising 28,337 bp for Pyrobaculum spherical virus.

Proteins

Virions contain a major structural protein with molecular mass of about 33 kDa and two minor proteins of about 16 and 20 kDa. About 80% of amino acids of the major structural protein are hydrophobic. There are 38–48 predicted proteins encoded on viral genomes, none of which shows any sequence similarity to proteins in extant databases.

Lipids

Virion contains modified host lipids.

Carbohydrates

None reported.

Genome organization and replication

The genome is linear dsDNA (Figure 2). The ends of the linear genome carry inverted repeat sequences (190 bp long for Pyrobaculum spherical virus), which contain multiple copies of short direct repeats. Almost all recognizable genes are located on one DNA strand. Several examples of gene duplication occur. No information is available about genome replication.

Antigenic properties

Not known.

Biological properties

The hosts are members of the hyperthermophilic archaeal genera Pyrobaculum and Thermoproteus. They are strict aerobes thriving in extreme geothermal environments with temperatures around 85 °C, pH 6. The infection does not cause lysis of host cells and is noncytocidal. The viral genome does not integrate into the host chromosome.

Species demarcation criteria in the genus

Species in the genus differ in virion size, host range, size and nucleotide sequence of the genome.

List of species in the genus Globulovirus

Species names are in italic script; names of strains are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.

List of other related viruses which may be members of the genus Globulovirus but have not been approved as species

None reported.

List of unassigned species in the family Globuloviridae

None reported.

Phylogenetic relationships within the family

Not applicable.

Similarity with other taxa

Not known.

Derivation of name

Globulo: from Latin globulus, “small ball”.

Further reading

Ahn, D.-G., Kim, S.-I., Rhee, J.-K., Kim, K. P., Pan, J.-G. and Oh, J.-W. (2006). TTSV1, a new virus-like particle isolated from the hyperthermophilic crenarchaeote Thermoproteus tenax. Virology 351, 280-290.

Häring, M., Peng, X., Brügger, K., Rachel, R., Stetter, K.O., Garrett, R.A. and Prangishvili, D. (2004). Morphology and genome organisation of the virus PSV of the hyperthermophilic archaeal genera Pyrobaculum and Thermoproteus: a novel virus family, the Globuloviridae. Virology 323, 233-242.

Prangishvili, D., Forterre, P. and Garrett, R.A. (2006). Viruses of the Archaea: a unifying view. Nat. Rev. Microbiol. 4, 837-848.

Prangishvili, D., Garrett, R.A. and Koonin, E.V. (2006). Evolutionary genomics of archaeal viruses: Unique viral genomes in the third domain of life. Virus Res. 117, 52-67.

Contributed by

Prangishvili, D.