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

Abstract

Zeus' Revenge Sediment-dwelling amoebae appear to have an unhappy affinity for huge viruses. Giant icosahedral Mimiviruses with genomes of the order of 1 megabase (Mb) were first identified in Acanthamoeba. Digging into antipodean sediments has once again been fruitful where Philippe et al. (p. 281 ; see the cover) discovered some enormous viruses in Acanthamoeba, visible by light microscopy and having genomes up to 2.5 Mb. The Pandoraviruses are phagocytosed by target cells and, after fusing with the phagosome membrane, their contents are released into the cytoplasm where they wreak terrible havoc on its nucleus. These viruses are encased into a tegument-like envelope and lack genes for capsid proteins, and there are no genes for protein translation, adenosine triphosphate generation, or binary fission—confirming their classification as viruses.