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Pandoraviruses are highly derived phycodnaviruses.

Natalya Yutin, Eugene V Koonin1

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Phylogenetic analysis reveals Pandoraviruses, the largest viruses, are highly derived phycodnaviruses, not closely related to other giant viruses. This suggests giant viruses evolved independently multiple times from smaller nucleocytoplasmic large DNA viruses.

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Area of Science:

  • Virology
  • Genomics
  • Evolutionary Biology

Background:

  • Pandoraviruses are exceptionally large viruses with massive genomes, surpassing many bacteria and archaea.
  • Their phylogenetic relationship to other large DNA viruses (NCLDV) and giant viruses like Mimiviridae is unclear.
  • Pandoraviruses lack some core NCLDV genes, further complicating their classification.

Purpose of the Study:

  • To determine the evolutionary origins and phylogenetic placement of Pandoraviruses.
  • To clarify the relationship between Pandoraviruses and other known viral families, particularly Phycodnaviridae and Mimiviridae.

Main Methods:

  • Phylogenetic analysis using six core nucleocytoplasmic large DNA virus (NCLDV) genes.
  • Comparative genomic analysis to identify shared and divergent genetic elements.

Main Results:

  • Phylogenetic analysis confidently places Pandoraviruses within the Phycodnaviridae family.
  • Pandoraviruses exhibit a specific affinity with Coccolithoviruses, a subgroup within Phycodnaviridae.
  • Despite unique features, Pandoraviruses are identified as highly derived members of this family.

Conclusions:

  • Pandoraviruses represent a highly evolved lineage within the Phycodnaviridae family.
  • The findings suggest that giant viruses have evolved independently from smaller NCLDV on at least two separate occasions.
  • This challenges previous assumptions about the monophyly of giant viruses.