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Sukunaarchaeum keeps its copying machinery in a stripped-down genome

A newly published peer-reviewed study describes Sukunaarchaeum, an archaeon whose unusually small genome retains the machinery for copying and using genetic information while lacking most recognizable nutrient and energy pathways. The finding extends earlier preprint work on a marine microbial community. It suggests strong dependence on another organism, although the cell's appearance and its relationship with a host remain unobserved.

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A clear seawater bottle connected by tubing to a membrane filter on a wet sampling table beside a rocky coast.

Replication survives extensive genome reduction

Sukunaarchaeum retains the machinery needed to copy and use genetic information despite losing most recognizable pathways for producing nutrients and energy. The microorganism is an archaeon, part of a group of single-celled organisms distinct from bacteria. Its unusually small genome concentrates the remaining functions on genetic information processing.[1], [2]

The newly published peer-reviewed Current Biology study describes this extensive genome reduction. The remaining genes include core machinery for DNA copying, RNA production and protein synthesis. The missing metabolic functions suggest strong dependence on another organism for essential materials. That relationship remains an interpretation of the genome: the cell's appearance and its connection to a particular host have not yet been observed.[1]

A marine sample yielded a circular DNA sequence

The authors' May 2025 preprint traced the genome to a community associated with Citharistes regius, a marine microorganism sampled off Shimoda, Japan. It described a circular sequence of 238,000 base pairs and 189 protein-coding genes. Assemblies using short and long DNA reads supported the same circular structure. These details belong to the earlier preprint account of the study.[1]

Unknown proteins occupy a large share of the genome

In the preprint, genes for large proteins of unknown function occupied about a quarter of the genome. Computational predictions associated them with the cell membrane; a role in host interactions remains a hypothesis. Related sequences in other marine genetic datasets suggest a wider lineage beyond the original sample. Evolutionary analyses leave its exact position among archaea unresolved.[1]

References

  1. News sourceUniversity of TsukubaA tiny archaeal genome separates replication machinery from metabolism
    Primary preprintbioRxivA cellular entity retaining only its replicative core: Hidden archaeal lineage with an ultra-reduced genome
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  2. News sourceLaboratory NewsSukunaarchaeum retains copying machinery after extensive genome reduction↩
Space and explorationEnergy transition and climate

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