Photosynthetic cryptophytes are ubiquitous protists that are major participants in the freshwater phytoplankton bloom at the onset of spring. Mortality due to change in environmental conditions and grazing have been recognized as key factors contributing to bloom collapse. In contrast, the role of viral outbreaks as factors terminating phytoplankton blooms remains unknown from freshwaters. Here, we isolated and characterized a cryptophyte virus contributing to the annual collapse of a natural cryptophyte spring bloom population. This viral isolate is also representative for a clade of abundant giant viruses (phylum Nucleocytoviricota) found in freshwaters all over the world.

• Klíčová slova
• Imitervirales, NCLDVs, Nucleocytoviricota, cryptophytes, freshwater giant viruses, giant viruses, phytoplankton spring bloom, viral isolation,
• MeSH
• Cryptophyta genetika   MeSH
• Eukaryota MeSH
• fytoplankton MeSH
• lidé MeSH
• obří viry * MeSH
• viry * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

The diverse GTPases of the dynamin superfamily play various roles in the cell, as exemplified by the dynamin-related proteins (DRPs) Mgm1 and Opa1, which remodel the mitochondrial inner membrane in fungi and metazoans, respectively. Via an exhaustive search of genomic and metagenomic databases, we found previously unknown DRP types occurring in diverse eukaryotes and giant viruses (phylum Nucleocytoviricota). One novel DRP clade, termed MidX, combined hitherto uncharacterized proteins from giant viruses and six distantly related eukaryote taxa (Stramenopiles, Telonemia, Picozoa, Amoebozoa, Apusomonadida, and Choanoflagellata). MidX stood out because it was not only predicted to be mitochondria-targeted but also to assume a tertiary structure not observed in other DRPs before. To understand how MidX affects mitochondria, we exogenously expressed MidX from Hyperionvirus in the kinetoplastid Trypanosoma brucei, which lacks Mgm1 or Opa1 orthologs. MidX massively affected mitochondrial morphology from inside the matrix, where it closely associates with the inner membrane. This unprecedented mode of action contrasts to those of Mgm1 and Opa1, which mediate inner membrane remodeling in the intermembrane space. We speculate that MidX was acquired in Nucleocytoviricota evolution by horizontal gene transfer from eukaryotes and is used by giant viruses to remodel host mitochondria during infection. MidX's unique structure may be an adaptation for reshaping mitochondria from the inside. Finally, Mgm1 forms a sister group to MidX and not Opa1 in our phylogenetic analysis, throwing into question the long-presumed homology of these DRPs with similar roles in sister lineages.

• Klíčová slova
• Nucleocytoviricota, Mgm1, Opa1, dynamin superfamily, mitochondria, protists,
• MeSH
• dynaminy genetika   metabolismus   MeSH
• fylogeneze MeSH
• mitochondriální proteiny genetika   metabolismus   MeSH
• mitochondrie genetika   metabolismus   MeSH
• obří viry * genetika   metabolismus   MeSH
• Saccharomyces cerevisiae genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• dynaminy MeSH
• mitochondriální proteiny MeSH