Filling Knowledge Gaps for Mimivirus Entry, Uncoating, and Morphogenesis.

Area of Science:

• * Virology
• * Cell Biology
• * Microbiology

Background:

• * Mimivirus, a giant virus, presents unique structural and genomic characteristics.
• * Its replication cycle, particularly entry, uncoating, and morphogenesis, remains incompletely understood.
• * Previous studies have proposed various models for mimivirus replication, but gaps in knowledge persist.

Purpose of the Study:

• * To elucidate unclear aspects of the mimivirus replication cycle, focusing on entry, uncoating, and morphogenesis.
• * To investigate the role of phagocytosis and phagosome acidification in mimivirus infection.
• * To clarify the process of capsid assembly and fibril acquisition during mimivirus replication.

Main Methods:

• * Extensive analysis of electron microscope images.
• * Biological assays, including treatment with cytochalasin (phagocytosis inhibitor) and bafilomicin (phagosome acidification inhibitor).
• * Examination of viral particle morphogenesis and assembly within infected Acanthamoeba castellanii.

Main Results:

• * Cytochalasin treatment inhibited mimivirus particle incorporation and viral growth, confirming phagocytosis-dependent entry.
• * Bafilomicin treatment impaired mimivirus uncoating and replication, indicating the necessity of phagosome acidification.
• * Morphogenesis analysis revealed capsid assembly from lamellar structures and simultaneous acquisition of genome and fibrils.
• * Defective mimivirus particles were observed even without the presence of virophages.

Conclusions:

• * Mimivirus entry into Acanthamoeba castellanii is mediated by phagocytosis.
• * Phagosome acidification is crucial for mimivirus uncoating and subsequent replication.
• * Mimivirus assembly involves a distinct process of capsid formation and simultaneous genome/fibril acquisition.
• * The study provides an updated model for the mimivirus replication cycle, incorporating new findings on entry, uncoating, and morphogenesis.