The Concept of Virus in the Giant Virus Era  

Résumé de la présentation:
The discovery of mimivirus in 2003 broadened the frontier of virology by revealing the existence of giant viruses with particle sizes and gene contents akin to that of cellular microbes. As we thought we were finally reaching the limit of viral complexity and started to build a new paradigm about the evolution of DNA viruses, the discovery of the pandoraviruses came ruining this newly built theoretical edifice. With 1.2 micron-long particles packing genomes up to 2.5 Mbp encoding a vast majority of proteins unique to the family, now surpassing the complexity of the smallest eukaryotic cells. As the family expanded with new members from all around the world and diverse environments, it clearly represent a class of giant viruses totally unrelated to the Megaviridae. I will also present the discovery of pithovirus sibericum, isolated from a >30,000-y-old radiocarbon-dated sample of Siberian permafrost that also share the amphora-shaped particles with the pandoraviruses. This family is also rapidly increasing with now modern members dividing the family in 3 clades. Mollivirus sibericum, isolated from the same permafrost sample, and a modern member, mollivirus kemtchatka, recently characterized. Pandoravirus-like particles may thus be associated with a variety of virus families more diverse than previously envisioned. To conclude, I will briefly present recent findings on the genome organization in the Mimiviridae and Marseilleviridae families, questioning on the origin and evolution of DNA viruses and their possible link with the emergence of eukaryotes.