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

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.

Evolution of viruses and cells: do we need a fourth domain of life to explain the origin of eukaryotes?

“…Nevertheless, its size record held for just a short time, as other, even bigger, giant viruses were soon discovered [23]. Today, three main lineages of giant viruses are known: Mimiviridae [21,[23][24][25], pithovirus [26] and Pandoraviridae [27]. The latter have the largest genomes, up to 2.77 Mbp [27], but all of them have genomes of more than 500 kbp.…”

“…Today, three main lineages of giant viruses are known: Mimiviridae [21,[23][24][25], pithovirus [26] and Pandoraviridae [27]. The latter have the largest genomes, up to 2.77 Mbp [27], but all of them have genomes of more than 500 kbp. In all cases, these genomes are composed of a large amount of ORFans accompanied by a relatively small fraction of genes with homologues in other viruses and/or in cellular organisms.…”

Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology

“…This assumption was radically challenged by the discovery of Pandoraviruses (9), which show different and somewhat opposite characteristics. These Acanthamoeba-infecting viruses exhibit much larger amphora-shaped virions 1-1.2 μm in length.…”

“…These Acanthamoeba-infecting viruses exhibit much larger amphora-shaped virions 1-1.2 μm in length. Their guaninecytosine (GC)-rich (>61%) genomes are up to 2.8 Mb long and encode up to 2,500 proteins sharing no resemblance with those of Megaviridae (9). Finally, Pandoravirus particles do not incorporate the transcription machinery that would allow them to entirely replicate in the host's cytoplasm.…”

Pithovirus sibericum : réveil d’un virus géant de plus de 30 000 ans

“…Alors que l'on commençait à penser que les virus géants appartiendraient tous à cette même grande famille de virus icosaédriques, est survenue la découverte des Pandoravirus, isolés d'abord au Chili dans le Pacifique, puis en Australie dans un étang d'eau douce [9]. Les tailles de ces virus et leurs génomes rivalisaient cette fois avec ceux du monde des eucaryotes.…”