Abstract
Giant viruses are a group of eukaryotic double-stranded DNA viruses with large virion and genome size that challenged the traditional view of virus. Newly isolated strains and sequenced genomes in the last two decades have substantially advanced our knowledge of their host diversity, gene functions, and evolutionary history. Giant viruses are now known to infect hosts from all major supergroups in the eukaryotic tree of life, which predominantly comprises microbial organisms. The seven well-recognized viral clades (taxonomic families) have drastically different host range. Mimiviridae and Phycodnaviridae, both with notable intrafamilial genome variation and high abundance in environmental samples, have members that infect the most diverse eukaryotic lineages. Laboratory experiments and comparative genomics have shed light on the unprecedented functional potential of giant viruses, encoding proteins for genetic information flow, energy metabolism, synthesis of biomolecules, membrane transport, and sensing that allow for sophisticated control of intracellular conditions and cell-environment interactions. Evolutionary genomics can illuminate how current and past hosts shape viral gene repertoires, although it becomes more obscure with divergent sequences and deep phylogenies. Continued works to characterize giant viruses from marine and other environments will further contribute to our understanding of their host range, coding potential, and virus-host coevolution.
Highlights
The Nucleo-Cytoplasmic Large DNA Viruses (NCLDVs) are a group of double-stranded DNA viruses of eukaryotes that was established two decades ago [1]
Nucleocytoviricota within the virus kingdom Bamfordvirae by the ICTV [3,4]. For their extraordinary genome size and virion size among all viruses, NCLDVs are commonly known as giant viruses [7,8,9,10,11], which reflects their distinction from traditionally defined viruses [12]
Recent advances in the biology of giant viruses have brought to the fore their expanded host range and coding potential, as shown in numerous studies based on isolation and cultivation, genomic and functional characterization, or environmental metagenomics
Summary
The Nucleo-Cytoplasmic Large DNA Viruses (NCLDVs) are a group of double-stranded DNA viruses of eukaryotes that was established two decades ago [1]. Nucleocytoviricota within the virus kingdom Bamfordvirae (realm Varidnaviria) by the ICTV [3,4]. For their extraordinary genome size (up to 2.8 Mb [5]) and virion size (up to 2.5 μm [6]) among all viruses, NCLDVs are commonly known as giant viruses [7,8,9,10,11], which reflects their distinction from traditionally defined viruses [12]. Recent advances in the biology of giant viruses have brought to the fore their expanded host range and coding potential, as shown in numerous studies based on isolation and cultivation, genomic and functional characterization, or environmental metagenomics. By considering NCLDVs—giant viruses—as a whole, here we briefly summarize and highlight recent findings that have revolutionized our view of their host range and coding potential, with particular emphasis on the evolutionary implications for giant viral genomes
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