Mimiviridae

Mimiviridae is a family of large DNA viruses that belong to the group known as nucleocytoplasmic large DNA viruses (NCLDVs). These viruses are notable for their large size and complex genomes, which challenge the traditional boundaries between viruses and cellular life.

Discovery and History

The first member of the Mimiviridae family, Mimivirus, was discovered in 1992 but was initially misidentified as a bacterium due to its large size. It was not until 2003 that it was correctly identified as a virus. The name "Mimivirus" is derived from "mimicking microbe" due to its bacterial-like size and appearance.

Morphology

Mimiviridae viruses are characterized by their large icosahedral capsids, which can reach up to 750 nm in diameter, making them some of the largest known viruses. The capsid is composed of a protein shell that encases the viral DNA and associated proteins. The surface of the capsid is often covered with fibrils, which may play a role in host cell attachment and entry.

Genome

The genome of Mimiviridae viruses is composed of double-stranded DNA and can be as large as 1.2 million base pairs, encoding over 1,000 proteins. This extensive genetic repertoire includes genes typically found in cellular organisms, such as those involved in DNA repair, protein folding, and even translation, which is unusual for viruses.

Host Range and Ecology

Mimiviridae primarily infect amoebae, particularly species of the genus Acanthamoeba. These viruses are found in a variety of environments, including freshwater, marine, and soil ecosystems. Their presence in diverse habitats suggests they play a significant role in microbial ecology and nutrient cycling.

Replication Cycle

The replication cycle of Mimiviridae begins with the attachment of the virus to the host cell surface, followed by entry into the host cytoplasm. Once inside, the viral genome is released and transcription begins. The virus assembles in cytoplasmic viral factories, where new virions are produced and eventually released to infect new host cells.

Significance and Impact

The discovery of Mimiviridae has expanded our understanding of viral diversity and evolution. Their large genomes and complex biology challenge the traditional definitions of viruses and have implications for the study of the origin of life. Additionally, Mimiviridae serve as a model for studying virus-host interactions and the evolution of large DNA viruses.

Also see

• Nucleocytoplasmic large DNA viruses
• Mimivirus
• Acanthamoeba
• Virus classification