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A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont


According to small subunit ribosomal RNA (ss rRNA) sequence comparisons all known Archaea belong to the phyla Crenarchaeota, Euryarchaeota, and—indicated only by environmental DNA sequences—to the ‘Korarchaeota’1,2. Here we report the cultivation of a new nanosized hyperthermophilic archaeon from a submarine hot vent. This archaeon cannot be attached to one of these groups and therefore must represent an unknown phylum which we name ‘Nanoarchaeota’ and species, which we name ‘Nanoarchaeum equitans’. Cells of ‘N. equitans’ are spherical, and only about 400 nm in diameter. They grow attached to the surface of a specific archaeal host, a new member of the genus Ignicoccus3. The distribution of the ‘Nanoarchaeota’ is so far unknown. Owing to their unusual ss rRNA sequence, members remained undetectable by commonly used ecological studies based on the polymerase chain reaction4. ‘N. equitans’ harbours the smallest archaeal genome; it is only 0.5 megabases in size. This organism will provide insight into the evolution of thermophily, of tiny genomes and of interspecies communication.

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Figure 1: Electron microscopy and fluorescence light microscopy of the ‘Nanoarchaeum equitans’–Ignicoccus sp. coculture.
Figure 2: Southern blot analysis of DNA from Ignicoccus sp. and the ‘N. equitans’–Ignicoccus sp. coculture, treated with restriction enzymes.
Figure 3: Secondary structure model for the ss rRNA of ‘N. equitans’.


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We thank W. Ludwig and D. Prangishvili for stimulating discussions, S. Diller, S. Leptihn, M. Brandl, I. Wyschkony and P. Hummel for technical support, and B. Hedlund for critically reading the manuscript. We are grateful to the cruise leader P. Stoffers, the crew of RV Poseidon and the submersible Jago team for support during sampling, and the Icelandic government for a research permit. This study was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.

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Correspondence to Karl O. Stetter.

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Huber, H., Hohn, M., Rachel, R. et al. A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont. Nature 417, 63–67 (2002).

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