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Abstract “Jumbo phages” are tailed phages with genome sizes >200 kbp and physical dimensions reaching up to 0.45 μm. Although jumbo phages represent only a small fraction of the isolated phages to date, metagenomic surveys have shown that they are broadly distributed in a wide range of environments. In this study, we surveyed metagenomic data from aquatic systems and identified 25 genomes from a heretofore-undescribed lineage of jumbo phages with genomes reaching up to 307 kbp. We refer to these phages as “moraphages”, from the Gaelic word ‘mór’, for large. Moraphages represent a diverse lineage with inter-genome average amino acid identity (AAI) ranging from 39 to 95%, and our pan-genomic analysis identified only 26 viral orthologous groups (VOGs) found in at least 80% of the genomes. Our phylogenomic analysis suggests that moraphages are distant relatives of a recently described lineage of huge phages from marine sediment. Moraphages lack much of the genetic machinery found in other lineages of large phages, but they have a range of genes that may be used to take over host cellular machinery and subvert host defenses, such as glutamine synthetases, antitoxin genes, and chaperones. The predicted hosts of most moraphages are members of the phylumBacteroidota, and some encode homologs of the chaperones DnaK and DnaJ that bear evidence of recent gene transfer from members of the orderFlavobacteriales. Our work sheds light on the emerging diversity of large phages that are found across the biosphere. 

Abstract The details surrounding the early evolution of eukaryotes and their viruses are largely unknown. Several key enzymes involved in DNA synthesis and transcription are shared between eukaryotes and large DNA viruses in the phylumNucleocytoviricota, but the evolutionary relationships between these genes remain unclear. In particular, previous studies of eukaryotic DNA and RNA polymerases often show deep-branching clades of eukaryotes and viruses indicative of ancient gene exchange. Here, we performed updated phylogenetic analysis of eukaryotic and viral family B DNA polymerases, multimeric RNA polymerases, and mRNA-capping enzymes to explore their evolutionary relationships. Our results show that viral enzymes form clades that are typically adjacent to eukaryotes, suggesting that they originate prior to the emergence of the Last Eukaryotic Common Ancestor (LECA). The machinery for viral DNA replication, transcription, and mRNA capping are all key processes needed for the maintenance of virus factories, which are complex structures formed by many nucleocytoviruses during infection, indicating that viruses capable of making these structures are ancient. These findings hint at a diverse and complex pre-LECA virosphere and indicate that large DNA viruses may encode proteins that are relics of extinct proto-eukaryotic lineages. 

Abstract Polinton-like viruses (PLVs) are a diverse group of small integrative dsDNA viruses that infect diverse eukaryotic hosts. Many PLVs are hypothesized to parasitize viruses in the phylum Nucleocytoviricota for their own propagation and spread. Here, we analyze the genomes of novel PLVs associated with the occlusion bodies of entomopoxvirus (EPV) infections of two separate lepidopteran hosts. The presence of these elements within EPV occlusion bodies suggests that they are the first known hyperparasites of poxviruses. We find that these PLVs belong to two distinct lineages that are highly diverged from known PLVs. These PLVs possess mosaic genomes, and some essential genes share homology with mobile genes within EPVs. Based on this homology and observed PLV mosaicism, we propose a mechanism to explain the turnover of PLV replication and integration genes.