Giant virus discovered in Pacific Ocean with the longest tail ever recorded

Scientists exploring the North Pacific Subtropical Gyre have uncovered a giant virus with a tail longer than any seen before.

Dubbed PelV-1, the virus infects a type of plankton called Pelagodinium and boasts a 2.3-micrometer-long tail, roughly 19 times longer than the coronavirus responsible for COVID-19. Its 200-nanometer capsid is dwarfed by the unprecedented appendage, which researchers say may help the virus attach to and enter host cells.

While most viruses either lack tails or have tiny ones, PelV-1’s structure is unique. Time-lapse imaging shows the tail attaching to plankton cells during infection, yet newly formed viruses inside the cells appear tail-less, suggesting the appendage forms only after the virus exits its host.


PelV-1 was discovered at Station ALOHA, a long-term monitoring site north of Hawaii. Scientists collected seawater from 25 meters below the surface, isolating the plankton and unexpectedly identifying the viral hitchhiker.

Viruses that infect dinoflagellates like Pelagodinium are extremely rare; only two other large DNA viruses are known to target this group. Understanding these viruses could shed light on energy flow, nutrient cycles, and even harmful algal blooms in ocean ecosystems.

The genome of PelV-1 is massive for a virus, with 467 genes across 459,000 base pairs. Remarkably, some of these genes are typically found only in living cells, including parts of energy production cycles, light-harvesting proteins, and rhodopsins, light-sensitive molecules that may help the virus capture sunlight.

The study also revealed a second, rarer virus in the same culture, named co-PelV. Unlike PelV-1, it lacks a tail but carries metabolic genes that could alter its host’s behavior and energy use.

Future research will explore how PelV-1 assembles its tail, the role it plays in infection, and whether other long-tailed viruses exist in the oceans.