Cedratvirus, a Double-Cork Structured Giant Virus, is a Distant Relative of Pithoviruses

Abstract

Most viruses are known for the ability to cause symptomatic diseases in humans and other animals. The discovery of Acanthamoeba polyphaga mimivirus and other giant amoebal viruses revealed a considerable and previously unknown area of uncharacterized viral particles. Giant viruses have been isolated from various environmental samples collected from very distant geographic places, revealing a ubiquitous distribution. Their morphological and genomic features are fundamental elements for classifying them. Herein, we report the isolation and draft genome of Cedratvirus, a new amoebal giant virus isolated in Acanthamoeba castellanii, from an Algerian environmental sample. The viral particles are ovoid-shaped, resembling Pithovirus sibericum, but differing notably in the presence of two corks at each extremity of the virion. The draft genome of Cedratvirus-589,068 base pairs in length-is a close relative of the two previously described pithoviruses, sharing 104 and 113 genes with P. sibericum and Pithovirus massiliensis genomes, respectively. Interestingly, analysis of these viruses' core genome reveals that only 21% of Cedratvirus genes are involved in best reciprocal hits with the two pithoviruses. Phylogeny reconstructions and comparative genomics indicate that Cedratvirus is most closely related to pithoviruses, and questions their membership in an enlarged putative Pithoviridae family.

Keywords: Acanthamoeba; Cedratvirus; Pithovirus; co-culture; double-cork; giant viruses; viral family.

Figure 1

Ultrathin electron microscopy imaging of the Cedratvirus replication cycle in Acanthamoeba castellanii. (a) Neo-phagocystis particle in vacuole; (b) Channel formation in first step of infection; (c) Empty particle 2 h post-infection (hpi) into a vacuole; (d–h) Various stages of concomitant Cedratvirus between 6 and 8 hpi in the cytoplasm of the amoeba; (i) Typical mature particle with the two corks.

Figure 2

Co-orthologous genes representing the current putative Pithoviridae family.

Figure 3

Unrooted tree based on DNA-dependent RNA polymerase II subunit 1 amino acid sequences; bootstrap values inferior to 0.5 (50%) were collapsed, branch length was applied; colors indicate family or viral groups: blue was used for Mimiviridae and an extended group including Phaeocystis globosa virus; purple for Ascoviridae-Iridoviridae; grey for Marseilleviridae; red for Cedratvirus and pithoviruses; green for Phycodnaviridae, pandoraviruses, and Mollivirus sibericum and black color for African swine fever virus and Faustovirus.