In-depth study ofMollivirus sibericum, a new 30,000-y-old giant virus infectingAcanthamoeba

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 38; pp. E5327 - E5335
• Main Authors: Legendre, Matthieu, Lartigue, Audrey, Bertaux, Lionel, Jeudy, Sandra, Bartoli, Julia, Lescot, Magali, Alempic, Jean-Marie, Ramus, Claire, Bruley, Christophe, Labadie, Karine, Shmakova, Lyubov, Rivkina, Elizaveta, Couté, Yohann, Abergel, Chantal, Claverie, Jean-Michel
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences 22-09-2015
• ISSN: 0027-8424; 1091-6490

Acanthamoebaspecies are infected by the largest known DNA viruses. These include icosahedral Mimiviruses, amphora-shaped Pandoraviruses, andPithovirus sibericum, the latter one isolated from 30,000-y-old permafrost.Mollivirus sibericum, a fourth type of giant virus, was isolated from the same permafrost sample. Its approximately spherical virion (0.6-μm diameter) encloses a 651-kb GC-rich genome encoding 523 proteins of which 64% are ORFans; 16% have their closest homolog in Pandoraviruses and 10% inAcanthamoeba castellaniiprobably through horizontal gene transfer. The Mollivirus nucleocytoplasmic replication cycle was analyzed using a combination of “omic” approaches that revealed how the virus highjacks its host machinery to actively replicate. Surprisingly, the host’s ribosomal proteins are packaged in the virion. Metagenomic analysis of the permafrost sample uncovered the presence of both viruses, yet in very low amount. The fact that two different viruses retain their infectivity in prehistorical permafrost layers should be of concern in a context of global warming. Giant viruses’ diversity remains to be fully explored.