Candidatus Sukunaarchaeum mirabile
| "Candidatus Sukunaarchaeum mirabile" | |
|---|---|
Scientific classification 
| |
| Domain: | Archaea |
| Kingdom: | incertae sedis |
| Genus: | Sukunaarchaeum |
| Species: | "Ca. Sukunaarchaeum mirabile"
|
| Binomial name | |
| "Candidatus Sukunaarchaeum mirabile" Harada et al., 2025[1]
| |
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 dinoflagellate Citharistes 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]
Discovery and naming
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]
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.[1]: fig.1 Of the 134 proteins (table S2) with a known or probable homolog of known function, only 5 were not related to genome replication, including four that likely serve to integrate host molecules and one of unclear function. The remaining 55 proteins include some exceptionally large membrane proteins.[1]
Phylogeny
Phylogenetic analyses place the genus Sukunaarchaeum at a deeply basal level in the archaeal tree, showing kingdom-level divergence relative to established archaeal kingdoms. 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]
The Sukuna-clade archaeons appear to generally associate with Dinophysales (Dinophyceae), an order of dinoflagellates that include C. regius (based on rDNA and rRNA content in different water samples). The clade as a whole is unlikely to all be associated with C. regius, as most detections were in particle-size fractions larger than the C. regius cell.[1]
See also
References
- ^ a b c d e f Harada, Ryo; Nishimura, Yuki; Nomura, Mami; Yabuki, Akinori; Shiba, Kogiku; Inaba, Kazuo; Inagaki, Yuji; Nakayama, Takuro (2025-05-02), A cellular entity retaining only its replicative core: Hidden archaeal lineage with an ultra-reduced genome, bioRxiv 10.1101/2025.05.02.651781, doi:10.1101/2025.05.02.651781, retrieved 2025-06-26
- ^ Wilcox, Christie (2025-06-13). Microbe with bizarrely tiny genome may be evolving into a virus (Report). doi:10.1126/science.z7ekqxv.
- ^ Muñoz Velasco, Israel (2025-06-17). "El hallazgo de Candidatus Sukunaarchaeum mirabile, una Archaea con el genoma más pequeño hasta ahora descubierto – Laboratorio de Genómica Ambiental, Facultad de Ciencias, Universidad Nacional Autónoma de México" [The finding of Candidatus Sukunaarchaeum mirabile, an Archaea with the smallest genome hitherto discovered.] (in Spanish). National Autonomous University of Mexico. Retrieved 2025-06-26.
- ^ Cowing, Keith (2025-05-07). "Candidatus Sukunaarchaeum Mirabile Is A Novel Archaeon With An Unprecedentedly Small Genome". Astrobiology. Retrieved 2025-06-26.