Candidatus Sukunaarchaeum mirabile (provisional name) is a species of archaea of which only the DNA is known, but which already presents several particularities: it is a holoparasite of the dinoflagellateCitharistes regius (it is the first known parasitic archaea) and its DNA, the smallest known for an archaea, only codes for proteins necessary for its reproduction.[2]
The DNA of Sukunaarchaeum mirabile was discovered in 2024 during a systematic search for DNA contained in the cells of Citharistes regius, which harbor symbiotic cyanobacteria and parasitic bacteria.[1]
The proposed name for the genus, Sukunaarchaeum, is a reference to Sukunabikona ("renowned little lord"), a small Shinto deity associated with hot springs. The specific epithet, mirabile, means "astonishing, admirable, marvelous."
Features
The DNA of Sukunaarchaeum mirabile occurs as a circular molecule comprising 238 kilobase pairs (kbp), less than half the size of the smallest previously known archaeal DNA. This genome lacks almost all recognizable metabolic pathways, and primarily encodes the mechanisms of DNA replication, transcription, and translation.[3] This suggests an unprecedented level of metabolic dependence on the host, a condition that challenges functional distinctions between minimal cellular life and viruses.[4] With only two ribosomal genes, however, it apparently relies on its host's ribosomal machinery to reproduce.[5]
The genome of Sukunaarchaeum mirabile has a GC linkage rate of 28.9% and contains 222 genes, encoding 2 ribosomal RNAs, 31 transfer RNAs, and 189 proteins. Only five of these proteins are not related to genome replication, including four that likely serve to integrate host molecules and one of unknown function.
Phylogeny
Phylogenetic analyses place the genus Sukunaarchaeum at a deeply basal level in the archaeal tree. Environmental DNA sequences indicate that sequences closely related to Sukunaarchaeum form a diverse clade, previously neglected in microbial studies. The discovery of Sukunaarchaeum pushes the conventional boundaries of cellular life and uncovers unexplored biological novelty in microbial interactions, suggesting that further exploration of symbiotic systems may reveal even more extraordinary life forms capable of reshaping our understanding of cellular evolution.[1]
↑ Nels Elde and Vincent Racaniello (June 18, 2025). "TWiEVO 115: Even the archaea are going viral". This Week in Evolution (Podcast). Microbe.tv. Event occurs at 01:02:20. Retrieved 2025-06-28.
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