title: Genome of Phaeocystis globosa virus PgV-16T highlights the common ancestry of the largest known DNA viruses infecting eukaryotes.
abstract: Large dsDNA viruses are involved in the population control of many globally distributed species of eukaryotic phytoplankton and have a prominent role in bloom termination. The genus Phaeocystis (Haptophyta, Prymnesiophyceae) includes several high-biomass-forming phytoplankton species, such as Phaeocystis globosa, the blooms of which occur mostly in the coastal zone of the North Atlantic and the North Sea. Here, we report the 459,984-bp-long genome sequence of P. globosa virus strain PgV-16T, encoding 434 proteins and eight tRNAs and, thus, the largest fully sequenced genome to date among viruses infecting algae. Surprisingly, PgV-16T exhibits no phylogenetic affinity with other viruses infecting microalgae (e.g., phycodnaviruses), including those infecting Emiliania huxleyi, another ubiquitous bloom-forming haptophyte. Rather, PgV-16T belongs to an emerging clade (the Megaviridae) clustering the viruses endowed with the largest known genomes, including Megavirus, Mimivirus (both infecting acanthamoeba), and a virus infecting the marine microflagellate grazer Cafeteria roenbergensis. Seventy-five percent of the best matches of PgV-16T-predicted proteins correspond to two viruses [Organic Lake phycodnavirus (OLPV)1 and OLPV2] from a hypersaline lake in Antarctica (Organic Lake), the hosts of which are unknown. As for OLPVs and other Megaviridae, the PgV-16T sequence data revealed the presence of a virophage-like genome. However, no virophage particle was detected in infected P. globosa cultures. The presence of many genes found only in Megaviridae in its genome and the presence of an associated virophage strongly suggest that PgV-16T shares a common ancestry with the largest known dsDNA viruses, the host range of which already encompasses the earliest diverging branches of domain Eukarya.
authors.affiliation: Structural and Genomic Information Laboratory, Unité Mixte de Recherche 7256, Centre National de la Recherche Scientifique, Aix-Marseille Université, 13288 Marseille Cedex 9, France.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Santini
authors.forename: Sandra
authors.initials: S
authors.lastname: Jeudy
authors.forename: Julia
authors.initials: J
authors.lastname: Bartoli
authors.forename: Olivier
authors.initials: O
authors.lastname: Poirot
authors.forename: Magali
authors.initials: M
authors.lastname: Lescot
authors.forename: Chantal
authors.initials: C
authors.lastname: Abergel
authors.forename: Valérie
authors.initials: V
authors.lastname: Barbe
authors.forename: K Eric
authors.initials: KE
authors.lastname: Wommack
authors.forename: Anna A M
authors.initials: AA
authors.lastname: Noordeloos
authors.forename: Corina P D
authors.initials: CP
authors.lastname: Brussaard
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Claverie
mesh_terms: D002874:Chromosome Mapping; D020440:Gene Duplication; D016679:Genome, Viral; D058087:Haptophyta / Q000648:ultrastructure / Q000821:virology*; D008969:Molecular Sequence Data; D017862:Phycodnaviridae / Q000145:classification / Q000235:genetics* / Q000648:ultrastructure; D010802:Phylogeny; D010839:Phytoplankton / Q000648:ultrastructure / Q000821:virology; D020543:Proteome; D018626:Retroelements; D012526:Satellite Viruses / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics
chemical_list: D020543:Proteome; D018626:Retroelements; D014764:Viral Proteins
keywords: core gene; gene duplication; giant virus; horizontal gene transfer; mobile element