The Large Marseillevirus Explores Different Entry Pathways by Forming Giant Infectious Vesicles

Area of Science:

• Virology
• Cell Biology
• Microbiology

Background:

• Giant viruses typically require amoebal phagocytosis for replication, a process usually triggered by particles >500 nm.
• Marseillevirus marseillevirus (MsV) is an unusual giant virus that replicates in Acanthamoeba despite having a smaller capsid size (~250 nm).

Purpose of the Study:

• To investigate the replication cycle of Marseillevirus marseillevirus (MsV) in Acanthamoeba.
• To elucidate the mechanism by which MsV initiates its replication despite not meeting the typical size requirement for phagocytosis.

Main Methods:

• Virological assays
• Molecular assays
• Microscopic analyses (immunofluorescence, scanning electron microscopy, transmission electron microscopy)

Main Results:

• MsV forms giant vesicles containing numerous viral particles, enclosed by membranes from the amoebal endoplasmic reticulum.
• These giant vesicles stimulate amoebal phagocytosis via an acidification-independent process.
• MsV entry can occur through phagocytosis of grouped particles or an endosome-stimulated pathway triggered by single particles.

Conclusions:

• MsV utilizes a novel replication strategy involving the formation of infective giant vesicles.
• This mechanism allows MsV to infect Acanthamoeba without fulfilling the conventional >500 nm size prerequisite for giant virus phagocytosis.
• This study reports, for the first time, the formation of giant infective vesicles associated with a large DNA virus.