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.
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Science 19 July 2013: 281-286.
About the Cover
COVER Enhanced transmission electron microscopy image of a "Pandoravirus" particle (length: 1.2 micrometers). Despite obeying all criteria to discriminate viruses from cells (no ribosome, no adenosine triphosphate production, no division), these Acanthamoeba viruses, unrelated to previously recognized virus families, exhibit genomes of up to 2.5 megabases, encoding more genes than some microsporidia. Image: O. Poirot/Structural and Genomic Information Laboratory, CNRS Aix-Marseille Université