Pandoraviruses: Amoeba Viruses with Genomes Up to 2.5 Mb Reaching That of Parasitic Eukaryotes

TLDR

The discovery of Mimivirus expanded the known limits of viral size and genome complexity, prompting a reevaluation of the upper bounds of the viral world. The study aimed to isolate and describe two giant viruses from Chilean coastal waters and an Australian freshwater pond that show no morphological or genomic similarity to known virus families. Researchers sampled diverse aquatic environments and associated sediments worldwide to assess the diversity of Megaviridae. The two viruses possess 2.5‑ and 1.9‑megabase genomes, establishing them as the first members of the Pandoravirus genus and the largest viral genomes reported to date.

Abstract

Ten years ago, the discovery of Mimivirus, a virus infecting Acanthamoeba, initiated a reappraisal of the upper limits of the viral world, both in terms of particle size (>0.7 micrometers) and genome complexity (>1000 genes), dimensions typical of parasitic bacteria. The diversity of these giant viruses (the Megaviridae) was assessed by sampling a variety of aquatic environments and their associated sediments worldwide. We report the isolation of two giant viruses, one off the coast of central Chile, the other from a freshwater pond near Melbourne (Australia), without morphological or genomic resemblance to any previously defined virus families. Their micrometer-sized ovoid particles contain DNA genomes of at least 2.5 and 1.9 megabases, respectively. These viruses are the first members of the proposed "Pandoravirus" genus, a term reflecting their lack of similarity with previously described microorganisms and the surprises expected from their future study.