Giant viruses continue to invade the world of virology, in gigantic genome sizes and various particles shapes. Strains discoveries and metagenomic studies make it possible to reveal the complexity of these microorganisms, their origins, ecosystems and putative roles. We isolated from a rat stool sample a new giant virus “Orpheovirus IHUMI-LCC2,” using Vermamoeba vermiformis as host cell. In this paper, we describe the main genomic features and replicative cycle of Orpheovirus IHUMI-LCC2. It possesses a circular genome exceeding 1.4 Megabases with 25% G+C content and ovoidal-shaped particles ranging from 900 to 1300 nm. Particles are closed by at least one thick membrane in a single ostiole-like shape in their apex. Phylogenetic analysis and the reciprocal best hit for Orpheovirus show a connection to the proposed Pithoviridae family. However, some genomic characteristics bear witness to a completely divergent evolution for Orpheovirus IHUMI-LCC2 when compared to Cedratviruses or Pithoviruses.

Vermamoeba vermiformis is a predominant free-living amoeba in human environments and amongst the most common amoebae that can cause severe infections in humans. it is a niche for numerous amoeba-resisting microorganisms such as bacteria and giant viruses. Differences in the susceptibility to these giant viruses have been observed. V. vermiformis and amoeba-resisting microorganisms share a sympatric lifestyle that can promote exchanges of genetic material. This work analyzed the first draft genome sequence of a V. vermiformis strain (CDC-19) through comparative genomic, transcriptomic and phylogenetic analyses. the genome of V. vermiformis is 59.5 megabase pairs in size, and 22,483 genes were predicted. A high proportion (10% (n = 2,295)) of putative genes encoded proteins showed the highest sequence homology with a bacterial sequence. the expression of these genes was demonstrated for some bacterial homologous genes. In addition, for 30 genes, we detected best BLAST hits with members of the Candidate Phyla Radiation. Moreover, 185 genes (0.8%) best matched with giant viruses, mostly those related to the subfamily Klosneuvirinae (101 genes), in particular Bodo saltans virus (69 genes). Lateral sequence transfers between V. vermiformis and amoeba-resisting microorganisms were strengthened by Sanger sequencing, transcriptomic and phylogenetic analyses. This work provides important insights and genetic data for further studies about this amoeba and its interactions with microorganisms. Amoebozoa species are widely distributed in different environments from terrestrial to aquatic ecosystems, where they can play important ecological roles 1,2. Members of the family Hartmannellidae are frequently detected along with a few other amoebae belonging to different genera of the taxon Amoebozoa 3. Vermamoeba vermiformis, a free-living amoeba of the family Hartmannellidae, formerly named Hartmannella vermiformis, was first isolated in freshwater from the Pigeon Lake, Wisconsin, and the Kankakee River, Indiana (United States) 4. V. vermiformis was thereafter commonly found in fresh surface water 5 , and also in tap water, bottled mineral water, thermal water, and recreational water environments such as fountains and swimming pools 6-8. Its density in drinking water sources and biofilms is higher than that of Acanthamoeba castellanii 9. V. vermiformis has two-stage life, switching between trophozoite and cystic form 3. Free-living amoebae (FLA) are commonly in contact with animals including humans. V. vermiformis was found to be the predominant amoeba in human environments 10,11 , and has been isolated more frequently from different hospital water systems than Acanthamoeba spp. 12. This amoeba is of special interest for human health as it is able, along with other Amoebozoa members including Acanthamoeba spp., to cause severe infections such as human keratitis 13-15. Despite its prevalence in human environments and its pathogenicity in humans, the genome of V. vermiformis had not been sequenced.