Genus Lipothrixvirus
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Type Species |
Thermoproteus virus 1 |
(TTV1) |
Virion Properties
Morphology
Virions are rigid rods, 410 nm long and 38 nm in diameter, with protrusions arising asymmetrically from both ends. The envelope does not show structure in electron micrographs (Fig. 1). It contains a helical core. Thermoproteus virus 1 (TTV1) and Thermoproteus virus 2 (TTV2) yield a DNA containing core structure and a lipid-containing coat upon treatment with detergent.
Physicochemical and Physical Properties
Virion Mr is 3.3 
108. Virion buoyant density in CsCl is 1.25 g/cm3. Virions are stable at 100°C and a fraction remains viable after autoclaving at 120°C. The particles maintain their structure in 6M urea and 7M guanidine hydrochloride. Detergents, e.g. Triton X100 and octylglycoside, dissociate virions into viral cores, containing the DNA plus DNA-binding proteins, and viral envelopes, containing isopranyl ether lipid and coat protein. Virions contain about 3% (w/w) DNA, about 75% protein and about 22% isopranyl ether lipids.
Nucleic Acid
Virions contain one molecule of linear dsDNA; Mr 10 106 (15.9 kbp). About 85% (except the leftmost Cla l fragment) of the total sequence has been determined. The ends of the DNA molecule are masked in an unknown manner.
Proteins
Virions contain at least four proteins of the following sizes: TP1, Mr 12.9 103; TP2, Mr 16.3 103; TP3, Mr 18.1 103; and TP4, Mr 24.5 103. TP1 and TP2 are DNA-associated, TP3 is the envelope protein, and the location of TP4 in the virus particle is unknown. Only TP1 is a basic protein. TP3 is highly hydrophobic, TP4 hydrophilic. Additional minor proteins may be present. A fifth protein, TPX, carrying a C-terminal (thr, pro)n repeat, is present in infected cells in high amount, but absent in virus particle.
Lipids
The virion envelope contains the same lipids as the host membrane, essentially diphytanyl tetraether-lipids. The envelope has a bilayer structure. The phosphate residues of the phospholipids are oriented towards the inside, the glycosyl residues towards the outside of the particles.
Carbohydrates
Virions contain carbohydrate in their glycolipid.
Genome Organization and Replication
The genome contains several transcription units. So far, the function of only few genes is known, among them those encoding the four structural proteins (TP1 to TP4). There are two ORFs, encoding (TP)n and (PT)n, between which specific recombination occurs with high frequency. Their map positions are shown in the Cla 1 restriction map of the viral genome (Fig. 2).
Adsorption and infection appears to proceed via interaction of the tips of pili of the host with the terminal protrusions of the virus. Fragments of the viral genome have sometimes been found integrated in host genomes. Complete non-integrated virus DNA exists in the cell in linear form. The virions are released by lysis. Infection may be latent.
Biological Properties
Host Range
The host range is limited to the archaea Thermoproteus tenax and Desulfurolobus ambivalens, in the kingdom Crenarchaeota. Other rod-shaped DNA-containing viruses of similar morphology but different dimensions have been found associated with Thermoproteus cultures or have been observed by electron microscopy in waters from Icelandic solfataras but virus has not been cultivated from these sources.
List of Species Demarcation Criteria in the Family
The 2 Lipothrixvirus species differ in virion size and genome size.
List of Species in the Genus
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
Species in the Genus
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Thermoproteus virus 1 |
[X14855] |
(TTV1) |
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Thermoproteus virus 2 |
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(TTV2) |
Tentative Species in the Genus
None reported.
List of Unassigned Species in the Family
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Thermoproteus virus 3 |
(TTV3) |
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Desulfurolobus virus DAFV |
(DAFV) |
Phylogenetic Relationships within the Family
Not available.
Similarity with Other Taxa
None reported.
Derivation of Names
Lipo: from Greek, lipos, “fat”.
Thrix: from Greek, thrix, “hair”.
