Abstract
Nucleocytoplasmic large DNA viruses, or representatives of the proposed order Megavirales, include giant viruses of Acanthamoeba that were discovered over the last 12 years and are bona fide microbes. Phylogenies based on a few genes conserved amongst these megaviruses and shared by microbes classified as Eukarya, Bacteria, and Archaea, allowed for delineation of a fourth monophylogenetic group or “TRUC” (Things Resisting Uncompleted Classification) composed of the Megavirales representatives. A new Megavirales member named Pithovirus sibericum was isolated from a >30,000-year-old dated Siberian permafrost sample. This virion is as large as recently described pandoraviruses but has a genome that is approximately three to four times shorter. Our objective was to update the classification of P. sibericum as a new member of the “Fourth TRUC” club. Phylogenetic trees were constructed based on four conserved ancient genes and a phyletic analysis was concurrently conducted based on the presence/absence patterns of a set of informational genes from members of Megavirales, Bacteria, Archaea, and Eukarya. Phylogenetic analyses based on the four conserved genes revealed that P. sibericum is part of the fourth TRUC composed of Megavirales members, and is closely related to the families Marseilleviridae and Ascoviridae/Iridoviridae. Additionally, hierarchical clustering delineated four branches, and showed that P. sibericum is part of this fourth TRUC. Overall, phylogenetic and phyletic analyses using informational genes clearly indicate that P. sibericum is a new bona fide member of the “Fourth TRUC” club composed of representatives of Megavirales, alongside Bacteria, Archaea, and Eukarya.
Highlights
IntroductionNucleocytoplasmic large DNA viruses (NCLDVs), or members of the proposed order Megavirales, are the largest known viruses far; their genome ranges in size from ≈100 to 2500 kilobase pairs (kbp) and they are visible on photonic microscopy (Iyer et al, 2006; Raoult and Forterre, 2008; Yutin et al, 2009; Yutin and Koonin, 2012; Colson et al, 2013; Philippe et al, 2013; Legendre et al, 2014; Raoult, 2014)
In the phylogeny reconstruction based on DNA polymerase (DNApol) that is present in archaea, eukaryotes, and megaviruses, P. sibericum branched deeply in a cluster that included marseilleviruses, iridoviruses, and ascoviruses (Figure 3)
The present phylogenetic and phyletic analyses including P. sibericum suggests that this giant virus is linked to Megavirales, which comprises a monophyletic group alongside Eukarya, Bacteria, and Archaea
Summary
Nucleocytoplasmic large DNA viruses (NCLDVs), or members of the proposed order Megavirales, are the largest known viruses far; their genome ranges in size from ≈100 to 2500 kilobase pairs (kbp) and they are visible on photonic microscopy (Iyer et al, 2006; Raoult and Forterre, 2008; Yutin et al, 2009; Yutin and Koonin, 2012; Colson et al, 2013; Philippe et al, 2013; Legendre et al, 2014; Raoult, 2014). New member of the “4th TRUC” club include protists, algae, vertebrate animals, and insects They include giant viruses whose existence was revealed 12 years ago with the discovery of Mimivirus, a Acanthamoeba polyphagaresisting microbe that was initially considered a Gram positive bacterium (La Scola et al, 2003; Raoult et al, 2004) and discovered to have a gigantic 1200 kbp-large genome encompassing approximately 1000 genes (Raoult et al, 2007; Raoult, 2014). It is noteworthy that only a very weak homology with a major capsid protein from an unclassified megalocytivirus of the family Iridoviridae was found in the P. sibericum gene content
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
