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

TLDR

Giant DNA viruses, visible under a light microscope, include two distinct families: Megaviridae with pseudoicosahedral capsids and megabase-sized AT‑rich genomes, and Pandoraviruses with amphora‑shaped particles and up to 2.8 Mb GC‑rich genomes that infect unicellular protists. During a Siberian permafrost survey, the authors isolated a third giant virus that displays Pandoravirus morphology yet harbors gene content resembling icosahedral DNA viruses. The discovery indicates that pandoravirus‑like particles represent an unexplored diversity of unconventional DNA virus families.

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.