Pandoraviruses

Pandoraviruses are a genus of very large viruses, belonging to the family Pandoraveridae. Discovered in 2013, these viruses are notable for their exceptionally large genomes and particle size, which place them among the largest viruses known. Pandoraviruses infect amoebas, a type of single-celled organism. Their discovery challenged previous understandings of viral complexity and evolution.

The genome of pandoraviruses is significantly larger than most viruses, containing up to 2.5 million base pairs. This size is comparable to some parasitic bacteria. A substantial portion of the genes found in pandoraviruses are novel, with no known homologs in existing databases, suggesting a unique evolutionary path. This genetic novelty contributed to their initial classification as a distinct group.

Pandoravirus particles are also remarkably large, typically measuring up to 1 micrometer in length, making them visible under a light microscope. Their morphology is distinctive, often described as amphora-shaped or ovoid. The replication cycle of pandoraviruses occurs entirely within the cytoplasm of the host amoeba, unlike many other viruses that utilize the host cell's nucleus.

The initial discovery of pandoraviruses was made from samples collected from a freshwater lake in Chile (Pandoravirus chilensis) and later from marine sediments off the coast of Australia (Pandoravirus australiensis). Their existence highlights the vast and largely unexplored diversity of viruses in the environment and continues to be a subject of active research in virology and evolutionary biology.