PelV-1
Recent research in the North Pacific Subtropical Gyre has revealed a giant virus named PelV-1. This virus infects the plankton Pelagodinium and possesses a tail far longer than any previously identified. Measuring 2.3 micrometres, the tail is about 19 times the length of the coronavirus that causes COVID-19. This discovery provides new vital information about marine viruses and their ecological roles.
Discovery and Habitat
PelV-1 was found at Station ALOHA, north of Hawaii, by sampling seawater 25 metres below the surface. Scientists isolated Pelagodinium plankton and detected the virus as a hitchhiker. Viruses infecting dinoflagellates like Pelagodinium are extremely rare, with only two other large DNA viruses known to target this group.
Unique Morphology
PelV-1 has a 200-nanometre capsid and an exceptionally long tail measuring 2.3 micrometres. This tail is the longest viral appendage discovered to date. Unlike most viruses, which lack tails or have very small ones, PelV-1’s tail likely aids in attaching to and entering host cells. Time-lapse imaging shows the tail attaching to plankton cells during infection, but it disappears once the virus is inside, suggesting the tail forms only outside the host.
Genomic Features
The virus has a large genome of 459,000 base pairs containing 467 genes. Remarkably, some genes are typically found only in living cells. These include genes for energy production, light-harvesting proteins, and rhodopsins—molecules that capture sunlight. This suggests PelV-1 may use sunlight to power part of its lifecycle, fitting its habitat in sunlit ocean layers.
Ecological Importance
PelV-1 infects Pelagodinium, an important marine phytoplankton consumed by zooplankton and fish. About this virus helps explain energy flow and nutrient cycling in ocean ecosystems. It may also shed light on the dynamics of harmful algal blooms, which impact marine life and human health.
Related Viruses and Future Research
Alongside PelV-1, researchers discovered a rarer virus called co-PelV in the same culture. Co-PelV lacks a tail but carries metabolic genes that could influence host behaviour and energy use. Future studies aim to understand how PelV-1 assembles its tail and the role it plays in infection. Scientists also seek to find if other long-tailed viruses exist in the oceans.
Significance in Virology
Giant viruses like PelV-1 challenge traditional views of viruses. Discovered over 20 years ago, giant viruses are much larger than typical viruses and carry thousands of genes. These findings continue to reshape biological classifications and reveal new complexities in viral life.
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