Abstract
Extremely halophilic Archaea are the only known hosts for pleolipoviruses which are pleomorphic non-lytic viruses resembling cellular membrane vesicles. Recently, pleolipoviruses have been acknowledged by the International Committee on Taxonomy of Viruses (ICTV) as the first virus family that contains related viruses with different DNA genomes. Genomic diversity of pleolipoviruses includes single-stranded and double-stranded DNA molecules and their combinations as linear or circular molecules. To date, only eight viruses belong to the family Pleolipoviridae. In order to obtain more information about the diversity of pleolipoviruses, further isolates are needed. Here we describe the characterization of a new halophilic virus isolate, Haloarcula hispanica pleomorphic virus 4 (HHPV4). All pleolipoviruses and related proviruses contain a conserved core of approximately five genes designating this virus family, but the sequence similarity among different isolates is low. We demonstrate that over half of HHPV4 genome is identical to the genome of pleomorphic virus HHPV3. The genomic regions encoding known virion components are identical between the two viruses, but HHPV4 includes unique genetic elements, e.g., a putative integrase gene. The co-evolution of these two viruses demonstrates the presence of high recombination frequency in halophilic microbiota and can provide new insights considering links between viruses, membrane vesicles, and plasmids.
Highlights
Pleolipoviruses are rather newly-described, related pleomorphic viruses that infect extremely halophilic archaeal hosts from the genera Halorubrum, Haloarcula, or Halogeometricum [1]
A hazy plaque was isolated from the lawn of H. hispanica which had been inoculated with the culture supernatant of Haloferax sp. s5a–1
In order to confirm that the culture supernatant of Haloferax sp. s5a–1 induces plaque production, the spot assay was repeated, and plaques with similar appearance to those produced by Haloarcula hispanica pleomorphic virus 4 (HHPV4), were observed on the lawn of H. hispanica
Summary
Pleolipoviruses are rather newly-described, related pleomorphic viruses that infect extremely halophilic archaeal hosts from the genera Halorubrum, Haloarcula, or Halogeometricum [1]. In addition to the known pleolipoviruses, a number of related proviruses have been identified in the genomes of halophilic Archaea [3,4]. These proviruses, as well as all of the known pleolipoviruses, share a conserved core of four to five genes (or open reading frames (ORFs)) with varying degree of sequence similarity. While some of the genes in the conserved core defining the virus family remain unknown, others have been identified encoding, e.g., the viral major structural proteins, which include the spike and internal membrane protein, as well as a putative nucleoside triphosphatase (NTPase) [3,4,6]
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