AUTHOR=Sharma Vikas , Colson Philippe , Chabrol Olivier , Pontarotti Pierre , Raoult Didier 

TITLE=Pithovirus sibericum, a new bona fide member of the “Fourth TRUC” club

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00722

DOI=10.3389/fmicb.2015.00722

ISSN=1664-302X

ABSTRACT=<p>Nucleocytoplasmic large DNA viruses, or representatives of the proposed order <italic>Megavirales</italic>, include giant viruses of <italic>Acanthamoeba</italic> that were discovered over the last 12 years and are <italic>bona fide</italic> microbes. Phylogenies based on a few genes conserved amongst these megaviruses and shared by microbes classified as <italic>Eukarya, Bacteria</italic>, and <italic>Archaea</italic>, allowed for delineation of a fourth monophylogenetic group or “TRUC” (Things Resisting Uncompleted Classification) composed of the <italic>Megavirales</italic> representatives. A new <italic>Megavirales</italic> member named <italic>Pithovirus sibericum</italic> was isolated from a &gt;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 <italic>P. sibericum</italic> 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 <italic>Megavirales, Bacteria, Archaea</italic>, and <italic>Eukarya</italic>. Phylogenetic analyses based on the four conserved genes revealed that <italic>P. sibericum</italic> is part of the fourth TRUC composed of <italic>Megavirales</italic> members, and is closely related to the families <italic>Marseilleviridae and Ascoviridae/Iridoviridae</italic>. Additionally, hierarchical clustering delineated four branches, and showed that <italic>P. sibericum</italic> is part of this fourth TRUC. Overall, phylogenetic and phyletic analyses using informational genes clearly indicate that <italic>P. sibericum</italic> is a new <italic>bona fide</italic> member of the “Fourth TRUC” club composed of representatives of <italic>Megavirales</italic>, alongside <italic>Bacteria, Archaea</italic>, and <italic>Eukarya</italic>.</p>