Diversity, evolution, and classification of virophages uncovered through global metagenomics

Microbiome. 2019 Dec 10;7(1):157. doi: 10.1186/s40168-019-0768-5.


Background: Virophages are small viruses with double-stranded DNA genomes that replicate along with giant viruses and co-infect eukaryotic cells. Due to the paucity of virophage reference genomes, a collective understanding of the global virophage diversity, distribution, and evolution is lacking.

Results: Here we screened a public collection of over 14,000 metagenomes using the virophage-specific major capsid protein (MCP) as "bait." We identified 44,221 assembled virophage sequences, of which 328 represent high-quality (complete or near-complete) genomes from diverse habitats including the human gut, plant rhizosphere, and terrestrial subsurface. Comparative genomic analysis confirmed the presence of four core genes in a conserved block. We used these genes to establish a revised virophage classification including 27 clades with consistent genome length, gene content, and habitat distribution. Moreover, for eight high-quality virophage genomes, we computationally predicted putative eukaryotic virus hosts.

Conclusion: Overall, our approach has increased the number of known virophage genomes by 10-fold and revealed patterns of genome evolution and global virophage distribution. We anticipate that the expanded diversity presented here will provide the backbone for further virophage studies.

Keywords: Global distribution; Major capsid protein (MCP); Metagenomics; Virophage; Virophage classification; Virophage-NCLDV interactions.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • DNA, Viral / genetics*
  • Databases, Genetic
  • Genome, Viral / genetics*
  • Metagenome / genetics*
  • Metagenomics / methods*
  • Phylogeny
  • Virophages / classification*
  • Virophages / genetics


  • DNA, Viral