Inside the lifestyle of the virophage.
OBJECTIVE
We sought to better characterize Sputnik, the first isolated virophage, and to analyze its parasitic lifestyle during co-infection with Marseillevirus (a new giant virus) in Acanthamoeba castellanii.


METHODS
A combination of electron microscopy, immunofluorescence microscopy, and real-time PCR was used to characterize the kinetics of the viral replication cycle. RT-PCR was performed to detect RNAs inside the Sputnik virions.


RESULTS
Sputnik is a new viral entity carrying an almost complete ready-to-use set of viral RNAs (20 out of 21). Sputnik does not replicate with Marseillevirus but delays its replication cycle. While Marseillevirus is successfully internalized by A. castellanii following co-infections with Mamavirus and Sputnik, it does not initiate a replication cycle. In contrast, both Marseillevirus and Mamavirus can replicate in the amoeba in case of co-infection, but the development of one is exclusive from the other inside a single amoeba cell.


CONCLUSIONS
This work provides new insight into the Sputnik replication cycle with another giant virus and confirms that Sputnik is a virophage. It shows new dimensions of the interactions existing among giant viruses.
Desnues
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Unité de recherche sur les maladies infectieuses et tropicales émergentes, URMITE CNRS-IRD UMR 6236, Faculté de Médecine, Marseille, France. christelle.desnues@univmed.fr
Raoult
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D
D048248:Acanthamoeba castellanii / Q000821:virology*; D004267:DNA Viruses / Q000502:physiology*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012367:RNA, Viral / Q000032:analysis; D014771:Virion / Q000737:chemistry; D014779:Virus Replication
D012333:RNA, Messenger; D012367:RNA, Viral