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Scientists have discovered a microscopic organism that defies the very definition of life.

Known as Candidatus Sukunaarchaeum mirabile, this strange cellular entity lives in the ocean and possesses the smallest genome ever found in an archaeon — only ~238,000 base pairs.

Unlike normal cells, it has lost almost every metabolic function: it cannot make energy, build proteins, or survive on its own. Yet it still retains the genetic machinery required for replication and translation, such as ribosomal genes — a trait never seen in viruses.

That means it’s not fully alive like a cell, but not entirely non-living like a virus either. Scientists describe it as “a cellular entity retaining only its replicative core.”

This discovery could redefine what it means to be alive, shedding light on how early life might have evolved — and how it could exist in extreme or alien environments.

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🧬 Published in: A cellular entity retaining only its replicative core: Hidden archaeal lineage with an ultra-reduced genome
📚 Source: bioRxiv preprint, May 2025