TL;DR
Researchers have isolated a new giant DNA virus, ushikuvirus, from vermamoeba collected near Lake Ushiku in Japan. The virus shows unique capsid spikes and a replication strategy that disrupts the host nuclear membrane, a trait that may inform hypotheses about viruses contributing to eukaryotic cell evolution.
What happened
A joint team led by Professor Masaharu Takemura and collaborators at the National Institute of Natural Sciences reported the isolation and characterization of a new giant DNA virus named ushikuvirus. The isolate came from Lake Ushiku in Ibaraki Prefecture and infects vermamoeba, a type of amoeba. Morphologically it resembles members of the Mamonoviridae family—particularly medusavirus—with an icosahedral capsid bearing many short spikes. Ushikuvirus also displays distinctive features: multiple spiked structures capped with unique morphologies, some bearing filamentous extensions, and it induces a cytopathic effect that makes infected vermamoeba grow into unusually large cells. Unlike medusaviruses and clandestinovirus, which replicate within an intact host nucleus, ushikuvirus disrupts the nuclear membrane during particle production. The team published their findings in the Journal of Virology (Nov. 24, 2025), suggesting the new isolate sheds light on giant-virus diversity and may be relevant to theories about viral contributions to the emergence of eukaryotic cells.
Why it matters
- Adds a new data point to the diversity of giant DNA viruses that infect amoebae, expanding known host–virus relationships.
- The virus's distinct capsid structures and replication strategy offer comparative features relevant to viral eukaryogenesis hypotheses.
- Differences in how related giant viruses interact with host nuclei may illuminate evolutionary pathways between virus lineages and early eukaryotic cells.
- Understanding giant-virus–amoeba interactions could eventually inform approaches to amoeba-linked diseases, according to the researchers.
Key facts
- Ushikuvirus is a newly isolated giant DNA virus that infects vermamoeba.
- The virus was named after Lake Ushiku in Ibaraki Prefecture, Japan, where it was isolated.
- It has an icosahedral capsid with numerous spikes; some spikes have unique caps and filamentous extensions not seen in medusaviruses.
- Ushikuvirus causes infected vermamoeba to enlarge markedly, a specific cytopathic effect reported by the researchers.
- Unlike medusaviruses and clandestinovirus, which replicate inside an intact host nucleus, ushikuvirus disrupts the nuclear membrane to produce viral particles.
- The finding was reported online in the Journal of Virology on November 24, 2025 (DOI: 10.1128/jvi.01206-25).
- Research was led by Prof. Masaharu Takemura with team members from Tokyo University of Science and the National Institute of Natural Sciences.
- The work was supported by JSPS/KAKENHI (grant 20H03078) and a Joint Research ExCELLS program (No. 22EXC601-4).
- Related virus groups mentioned: Mamonoviridae (including medusavirus), clandestinovirus (infects vermamoeba) and comparisons to pandoravirus-like replication behaviors.
What to watch next
- Comparative phylogenetic and structural analyses of ushikuvirus and other Mamonoviridae-related viruses to clarify their evolutionary relationships.
- Further investigations into the molecular mechanism by which ushikuvirus disrupts the host nuclear membrane during particle assembly.
- Potential translational research exploring whether insights into giant-virus–amoeba interactions can inform prevention or treatment of amoeba-associated diseases (not confirmed in the source).
Quick glossary
- Giant virus: A group of large DNA viruses with genomes and particle sizes much bigger than typical viruses; many infect single-celled eukaryotes like amoebae.
- Eukaryote: An organism whose cells contain a membrane-bound nucleus and other organelles, including animals, plants, fungi and many unicellular species.
- Capsid: The protein shell that encloses a virus's genetic material; surface features such as spikes can affect host interactions.
- Virus factory: A specialized region in an infected cell where viral replication and assembly are concentrated; some are membrane-enclosed and may resemble cellular organelles.
- Cytopathic effect: Observable changes in a host cell caused by viral infection, such as cell enlargement, lysis or altered morphology.
Reader FAQ
What is ushikuvirus?
Ushikuvirus is a newly reported giant DNA virus that infects vermamoeba; it was isolated near Lake Ushiku in Japan.
How does ushikuvirus replicate inside its host?
The virus disrupts the host nuclear membrane to produce viral particles, differing from related viruses that replicate within an intact nucleus.
Does this discovery prove viruses created the eukaryotic nucleus?
The researchers say ushikuvirus adds support to the viral eukaryogenesis idea but does not constitute definitive proof.
Can ushikuvirus infect or harm humans?
Not confirmed in the source.
2026.01.07 Wednesday Ushikuvirus: A Newly Discovered Giant Virus May Offer Clues to the Origin of Life Ushikuvirus, an amoeba-infecting giant virus, joins the family of giant viruses that may have…
Sources
- Ushikuvirus: Newly discovered virus may offer clues to the origin of eukaryotes
- Ushikuvirus: Newly discovered giant virus may offer clues …
- Giant amoeba virus ushikuvirus sheds light on how …
- A Giant Virus From Japan Reignites a Radical Origin Story …
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