Genus: Betapleolipovirus


Genus: Betapleolipovirus

Distinguishing features

The circular double-stranded DNA genomes of betapleolipoviruses contain single-stranded discontinuities (Senčilo et al., 2012). The viruses have two ORFs encoding proteins with unknown function, which are not found in the genomes of members of the other genera.

Virion

Morphology

Virions are 55-70 nm in diameter and pleomorphic in shape with a membrane vesicle and irregularly distributed spike structures (Pietilä et al., 2012, Atanasova et al., 2012). Mature virions contain one or two types of internal membrane protein and a single type of spike protein.

Physicochemical and physical properties

Virions have a buoyant density of about 1.27-1.34 g cm−3 in CsCl (Pietilä et al., 2012). Virions are stable at a broad range of NaCl concentrations, from 0 M to 5.5 M (saturation) for at least 24 h at 4 °C, pH 7.2 (Demina et al., 2016), but are readily inactivated by temperatures above 60 °C, organic solvents and detergents. 

Nucleic acid

Betapleolipovirus genomes consist of a circular double-stranded DNA (~8.8 and 9.7 kbp; Halorubrum pleomorphic virus 3 (HRPV-3) and Halogeometricum pleomorphic virus 1 (HGPV-1) and contain single-stranded discontinuities (Senčilo et al., 2012).

Proteins

Virions contain two or three major structural proteins: one or two types of internal membrane protein (VP1 for HRPV-3; VP2 and VP3 for HGPV-1), and a spike protein (VP2 for HRPV-3; VP4 for HGPV-1) (Pietilä et al., 2012).

Lipids

Virions contain lipids derived non-selectively from host cell membranes. The major lipid species are PG and PGP-Me (Pietilä et al., 2012) . Virions of HRPV-3 also contain PGS, which has not been detected in HGPV-1 virions. The spike protein VP4 of HGPV-1 contains a lipid modification (Pietilä et al., 2012).

Genome organization and replication

The genomes of betapleolipoviruses encode either twelve or fifteen ORFs. Besides the conserved cluster of five genes or predicted ORFs shared among the members of the family Pleolipoviridae, betapleolipoviruses display high amino acid identity of two more putative ORF products. Both of these ORFs encode proteins of unknown function, one of which contains C-terminal winged helix-turn-helix (wHTH) domain, suggesting that it has a role linked to interaction with DNA (Senčilo et al., 2012). Similarly to other members of family Pleolipoviridae, betapleolipoviruses display a non-lytic life cycle and are thought to exit host cells via budding; albeit, HGPV-1 virion production does not retard the host growth and starts slightly later than those of other pleolipoviruses (Pietilä et al., 2012). 

Biology

Host range

Betapleolipoviruses infect only their original isolation hosts belonging to the family Halorubraceae or Haloferacaceae. HRPV-3 infects Halorubrum sp. SP3-3 and HGPV-1 infects Halogeometricum sp. CG-9 (Atanasova et al., 2012).

Geographical distribution

HRPV-3 and HGPV-1 with their own host strains have been isolated from Sedom Ponds, Israel and Cabo de Gata, Spain, respectively (Atanasova et al., 2012).

Species demarcation criteria

Not currently defined.

Member Species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus Abbreviation(s)Isolate Abbreviation
Halogeometricum virus HGPV1Halogeometricum pleomorphic virus 1JN882267NC_017090Complete genomeHGPV-1
Halorubrum virus HRPV3Halorubrum pleomorphic virus 3JN882265NC_017088Complete genomeHRPV-3

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.
Download GenBank/EMBL query for sequences listed in the table here.

Related, Unclassified Viruses

Virus name

Accession number

Abbreviation

Haloarcula hispanica pleomorphic virus 3

KX344510

HHPV-3

Natrinema virus SNJ2

AJVG01000023*

SNJ2

* Natrinema sp. J7-1 (Contig004) containing SNJ2 virus as a provirus.
Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.
Download GenBank/EMBL query for sequences listed in the table here.