New twigs on the third branch of life.

The single-celled microorganism Methanococcus jannaschii made headlines last month when scientists announced that they had fully sequenced its genes (SN: 8/24/96, p. 116). Interest in the microbe stems largely from its membership in a little-known group of microscopic organisms called the archaea. Neither bacteria nor eucarya (plants, animals, fungi, and any other organisms with a nucleus in their cells), archaea represent a third branch of life, many scientists contend.

This branch, relatively bare compared to the other two, has recently sprouted more twigs. In studies of a Yellowstone National Park hot spring called the Obsidian Pool, Susan M. Barns of Indiana University in Bloomington and her colleagues have unearthed signs of more than a dozen previously unknown archaea.

The researchers, who describe their work in the Aug. 20 Proceedings of the National Academy of Sciences, have not yet isolated the microorganisms. While studying sediment from the spring, the researchers discovered novel versions of a gene that encodes a subunit of ribosomes, the protein-making factories of cells. The genes resemble closely those of other archaea, but subtle differences in their DNA sequences indicate that they belong to new members of the archaean family, say the biologists.