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

Abstract

Significance Giant DNA viruses are visible under a light microscope and their genomes encode more proteins than some bacteria or intracellular parasitic eukaryotes. There are two very distinct types and infect unicellular protists such as Acanthamoeba . On one hand, Megaviridae possess large pseudoicosahedral capsids enclosing a megabase-sized adenine–thymine-rich genome, and on the other, the recently discovered Pandoraviruses exhibit micron-sized amphora-shaped particles and guanine–cytosine-rich genomes of up to 2.8 Mb. While initiating a survey of the Siberian permafrost, we isolated a third type of giant virus combining the Pandoravirus morphology with a gene content more similar to that of icosahedral DNA viruses. This suggests that pandoravirus-like particles may correspond to an unexplored diversity of unconventional DNA virus families.

Seasonal determinations of algal virus decay rates reveal overwintering in a temperate freshwater pond

“…For example, human enteric viruses persisted for several months when incubated in situ in dialysis bags filled with autoclaved marine water, and were most stable during winter months (Lo et al, 1976). Also, viruses have been shown to exist in high abundances in frozen Antarctic lakes (Foreman et al, 2011), viral genomes have been detected in~700-year-old frozen caribou feces (Ng et al, 2014), and even more incredible, a putatively 30 000-year-old giant virus of amoebas has been recovered from Siberian permafrost (Legendre et al, 2014). Hence, it is plausible, even likely, that reduced decay rates experienced during winter months may constitute a major mechanism for algal virus survival and the establishment of viral seed banks in many aquatic environments.…”

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.…”

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

“…Chose rare chez les virus, 10 % de leurs gènes comportent des introns qui requièrent la machinerie d'épissage nucléaire pour la maturation des transcrits. Ainsi, malgré une complexité géno-mique deux fois supérieure à celle des Mimiviridae, les Pandoravirus requièrent Pithovirus sibericum, « retour vers le futur » C'est dans ce contexte que surgit la découverte de Pithovirus sibericum dont la particule présente une morphologie ovoïde évoquant celles des Pandoravirus [12]. Nous nous attendions donc à ce qu'il s'agisse d'un autre Pandoravirus jusqu'à ce que l'analyse de son génome à ADN révèle qu'il ne présentait aucun lien phylogénétique avec les Pandoravirus.…”