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Discovery of undersea creature leads to new archaeal phylum


A new microbe has been discovered in an undersea hydrothermal vent off the coast of Iceland. The creature, named Nanoarchaeum equitans, is a member of the Archaea, the domain of life that is separate from plants, animals, and bacteria. The microbe does not fit any existing taxonomic groups, so the researchers who discovered it have proposed a new archaeal phylum called Nanoarchaeota, which stands for 'dwarf archaea.'

Cell of Ignicoccus spec. with four cells of Nanoarchaeum equitans attached. Electron micrograph. Freeze-etching. Bar 1 Ám.

The name Nanoarchaeum equitans means 'riding the fire sphere.' The microbe is spherical and tiny—only 400 nanometers in diameter (a nanometer is one-billionth of a meter). In addition to its small size, N. equitans has an extraordinarily small genome of 500,000 bases, on par with some of the smallest organisms on earth.

Karl O. Stetter, of the University of Regensburg, Germany, and colleagues discovered the new organism during a study of microbial communities living near hot vents. Temperatures near such vents approach the boiling point of water.

Hunting for possible new Nanoarchaeotes: Professor Karl O. Stetter takes samples from volcanic hot springs at Kamchatka, Eastern Siberia.

The researchers caught a first glimpse of N. equitans through an electron microscope in the laboratory. While viewing another archaeal species isolated from the vent—a new member of the genus Ignicoccus—they saw tiny dots attached to the cells of Ignicoccus. These dots turned out to be N. equitans. The two species probably have a symbiotic relationship; so far the researchers have not been able to grow N. equitans in culture without its host.

"With its tiny cell and genome size, 'Nanoarchaeum' resembles an intermediate between the smallest living organisms like Mycoplasma genitalium and big viruses like the pox virus and Chlorella virus CVK2," the researchers write in Nature. They note that the organism is "close to the theoretical minimum genome size calculated for a living being."

The precise evolutionary and phylogenetic position of Nanoarchaeum among the archaea is unclear and will have to be determined by future studies, according to Yan Boucher and W. Ford Doolittle of Dalhousie University in Halifax, Nova Scotia, who wrote a News and Views piece accompanying the study. Whatever its place, they conclude, "this is a genome begging to be sequenced."

In fact, Nanoarchaeum has now been sequenced. Since publication of the paper in Nature on May 2, Diversa, a biotechnology company in San Diego, California, and Celera in Rockville, Maryland, announced that they have together completed the genome of Nanoarchaeum.

For more images, see related Art Gallery Nanoarchaeota: New life under the sea

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Huber, H. et al. A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont. Nature 417, 63-67 (May 2, 2002).
Boucher, Y. & Doolittle, W.F. Biodiversity: Something new under the sea. Nature 417, 27-28 (May 2, 2002).

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