title: Mimivirus shows dramatic genome reduction after intraamoebal culture.
abstract: Most phagocytic protist viruses have large particles and genomes as well as many laterally acquired genes that may be associated with a sympatric intracellular life (a community-associated lifestyle with viruses, bacteria, and eukaryotes) and the presence of virophages. By subculturing Mimivirus 150 times in a germ-free amoebal host, we observed the emergence of a bald form of the virus that lacked surface fibers and replicated in a morphologically different type of viral factory. When studying a 0.40-μm filtered cloned particle, we found that its genome size shifted from 1.2 (M1) to 0.993 Mb (M4), mainly due to large deletions occurring at both ends of the genome. Some of the lost genes are encoding enzymes required for posttranslational modification of the structural viral proteins, such as glycosyltransferases and ankyrin repeat proteins. Proteomic analysis allowed identification of three proteins, probably required for the assembly of virus fibers. The genes for two of these were found to be deleted from the M4 virus genome. The proteins associated with fibers are highly antigenic and can be recognized by mouse and human antimimivirus antibodies. In addition, the bald strain (M4) was not able to propagate the sputnik virophage. Overall, the Mimivirus transition from a sympatric to an allopatric lifestyle was associated with a stepwise genome reduction and the production of a predominantly bald virophage resistant strain. The new axenic ecosystem allowed the allopatric Mimivirus to lose unnecessary genes that might be involved in the control of competitors.
authors.affiliation: Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 6236, Institut de Recherche pour le Développement, Faculté de Médecine, Université de la Méditerranée, 13385 Marseille Cedex 5, France.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Boyer
authors.forename: Saïd
authors.initials: S
authors.lastname: Azza
authors.forename: Lina
authors.initials: L
authors.lastname: Barrassi
authors.forename: Thomas
authors.initials: T
authors.lastname: Klose
authors.forename: Angélique
authors.initials: A
authors.lastname: Campocasso
authors.forename: Isabelle
authors.initials: I
authors.lastname: Pagnier
authors.forename: Ghislain
authors.initials: G
authors.lastname: Fournous
authors.forename: Audrey
authors.initials: A
authors.lastname: Borg
authors.forename: Catherine
authors.initials: C
authors.lastname: Robert
authors.forename: Xinzheng
authors.initials: X
authors.lastname: Zhang
authors.forename: Christelle
authors.initials: C
authors.lastname: Desnues
authors.forename: Bernard
authors.initials: B
authors.lastname: Henrissat
authors.forename: Michael G
authors.initials: MG
authors.lastname: Rossmann
authors.forename: Bernard
authors.initials: B
authors.lastname: La Scola
authors.forename: Didier
authors.initials: D
authors.lastname: Raoult
mesh_terms: D000656:Amoeba / Q000821:virology*; D000818:Animals; D018929:Cell Culture Techniques; D020285:Cryoelectron Microscopy; D017353:Gene Deletion; D016679:Genome, Viral; D006801:Humans; D051379:Mice; D056686:Mimiviridae / Q000235:genetics* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D020543:Proteome / Q000032:analysis; D015678:Viral Structural Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020543:Proteome; D015678:Viral Structural Proteins