A giant virus wags its tail

University of Hawai’i at Mānoa oceanographers have identified PelV-1, a dinoflagellate-infecting giant virus whose micron-length tail reaches 2.3 µm, stretching current notions of viral architecture.

Few phytoplankton-infecting viruses have been characterized, and dinoflagellate isolates remain scarce, leaving ocean-ecosystem models short of vital host-virus data. Prior surveys listed only two large DNA viruses infecting Heterocapsa species, neither accompanied by a genome sequence.

In the study, “A dinoflagellate-infecting giant virus with a micron-length tail,” published on the bioRxiv pre-print server, researchers combined electron microscopy and high-coverage sequencing to characterize PelV-1 infection of Pelagodinium sp.

Host cultures originated from Station ALOHA in the North Pacific Subtropical Gyre, where water sampled at 25 m yielded both the dinoflagellate and its virus.

Microscopy documented ~200 nm capsids and five morphotypes distinguished by two appendages: a 30 nm-wide tail extending up to 2.3 µm and a shorter, thicker protrusion positioned opposite a stargate capsid opening.

Time-series electron microscopy showed tails used for initial attachment but mature virions inside cells are non-tailed, supporting post-lysis tail assembly.

Results place PelV-1 and the rare co-PelV within Mesomimiviridae and detail 467 coding sequences plus nine tRNAs in PelV-1, alongside 569 genes and 14 tRNAs in co-PelV. Annotated genes span amino-acid, carbohydrate, lipid and TCA-cycle metabolism, light-harvesting complex, rhodopsin, ion channel, sugar transporters, aquaporin, tail-fiber homologs and encode cold-shock protein HSP70.

The authors propose that a 2.3 µm tail enhances host-encounter rates in the low-biomass gyre, inviting future work on how such structures shape plankton ecology.

PelV-1’s record-setting tail and broad metabolic arsenal expand the morphological and genomic diversity known for marine viruses.

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