Megavirus

Megavirus is a genus of nucleocytoplasmic large DNA viruses (NCLDVs) within the family Mimiviridae. The most well-known species within this genus is Megavirus chilensis, which was discovered off the coast of Chile in 2010. Megavirus is notable for its large size and complex genome, which challenges traditional definitions of viruses.

Discovery

Megavirus chilensis was discovered in 2010 by a team of French scientists led by Jean-Michel Claverie and Chantal Abergel. The virus was isolated from seawater samples collected off the coast of Las Cruces, Chile. The discovery was significant because it revealed a virus with a genome larger than that of any previously known virus, surpassing even the Mimivirus, which was discovered in 2003.

Structure

Megavirus particles are among the largest known viral particles, with a diameter of approximately 440 nanometers. The virion is composed of a protein capsid that encloses the viral DNA. The capsid is icosahedral in shape and is covered with a dense layer of fibrils, which are thought to play a role in host cell recognition and attachment.

Genome

The genome of Megavirus chilensis is composed of double-stranded DNA and is approximately 1.26 million base pairs in length. This genome size is larger than that of many small bacteria and contains over 1,100 predicted protein-coding genes. The genome encodes a variety of proteins involved in DNA replication, transcription, and translation, including some that are typically found only in cellular organisms.

Replication Cycle

Megavirus replicates within the cytoplasm of its host cell. The replication cycle begins with the attachment of the virus to the host cell surface, followed by entry into the cell. Once inside, the viral DNA is released into the cytoplasm, where it is transcribed and translated by the host's machinery. New viral particles are assembled in cytoplasmic viral factories, and mature virions are eventually released from the host cell, often resulting in cell lysis.

Host Range

Megavirus primarily infects amoebae, specifically species of the genus Acanthamoeba. These amoebae serve as natural hosts for the virus, providing the necessary cellular machinery for viral replication. The interaction between Megavirus and its host is complex and involves various mechanisms to evade host defenses.

Significance

The discovery of Megavirus has significant implications for our understanding of viral evolution and the origins of life. Its large genome and complex replication machinery suggest that it may have evolved from a more complex ancestor, possibly a cellular organism. This challenges the traditional view of viruses as simple entities and raises questions about the role of viruses in the evolution of life on Earth.

Also see

• Mimivirus
• Pandoravirus
• Nucleocytoplasmic large DNA viruses
• Acanthamoeba