A hidden archaeal lineage with an ultra-reduced genome retaining only its replicative core.

Candidatus Sukunaarchaeum mirabile, an archaeon with a 238 kbp genome, retains only its replicative core, representing the smallest known archaeal genome with cellular autonomy.

• Why it matters: Understanding how extreme genome reduction affects cellular independence is crucial for insights into minimal life forms and evolutionary limits of cellular autonomy, especially in host-associated microbes.
• What they did: Single-cell genomics uncovered Sukunaarchaeum from a dinoflagellate, revealing a highly divergent lineage with a genome lacking metabolic pathways but retaining DNA replication, transcription, and translation machinery.
• The result: The findings suggest that the informational core may define the lower limit for a self-replicating cell, challenging assumptions about the relationship between genome reduction and cellular dependence.