Comparison of a Modern and Fossil Pithovirus Reveals Its Genetic Conservation and Evolution

• Published in: Genome Biology and Evolution
• Main Authors: Levasseur, Anthony, Andreani, Julien, Delerce, Jeremy, Khalil, Jacques Bou, Robert, Catherine, La Scola, Bernard, Raoult, Didier
• Other Authors: Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes (URMITE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut National de la Santé et de la Recherche Médicale (INSERM)-IFR48, Institut des sciences biologiques (INSB-CNRS)-Institut des sciences biologiques (INSB-CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: [SDV.MHEP.MI]Life Sciences [q-bio]/Human health and pathology/Infectious diseases; permafrost
• Online Access: https://hal.archives-ouvertes.fr/hal-01455587; https://doi.org/10.1093/gbe/evw153

International audience Most theories on viral evolution are speculative and lack fossil comparison. Here, we isolated a modern Pithovirus-like virus from sewage samples. This giant virus, named Pithovirus massiliensis, was compared with its prehistoric counterpart, Pithovirus sibericum, found in Siberian permafrost. Our analysis revealed near-complete gene repertoire conservation, including horizontal gene transfer and ORFans. Furthermore, all orthologous genes evolved under strong purifying selection with a non-synonymous and synonymous ratio in the same range as the ratio found in the prokaryotic world. The comparison between fossil and modern Pithovirus species provided an estimation of the cadence of the molecular clock, reaching up to 3 x 10(-6) mutations/site/year. In addition, the strict conservation of HGTs and ORFans in P. massiliensis revealed the stablegenetic mosaicism in giant viruses and excludes the concept of a bag of genes. The genetic stability for 30,000 years of P. massiliensis demonstrates that giant viruses evolve similarly to prokaryotes by classical mechanisms of evolution, including selection and fixation of genes, followed by selective constraints.