A heat-loving archaeon capable of fixing nitrogen at a surprisingly hot 92 degrees Celsius, or 198 Fahrenheit, may represent Earths earliest lineages of organisms capable of nitrogen fixation, perhaps even preceding the kinds of bacteria today's plants and animals rely on to fix nitrogen.
The genetic analysis reported in the Dec. 15 issue of Science supports the notion that the gene needed to produce nitrogenase an enzyme capable of converting nitrogen gas, that's unusable by life, to a form like ammonia that is useable arose before the three main branches of life bacteria, archaea and eukaryotes diverged some 3.5 billion years ago, according to oceanographer Mausmi Mehta, who recently received her doctorate from the UW, and John Baross, UW professor of oceanography. This is opposed to the theory that the nitrogenase system arose within archaea and was later transferred laterally to bacteria.
"There's been lots of evidence that point to high-temperature archaea as the first life on Earth but the question has been, 'So why cant we find archaea that fix nitrogen at high temperatures"'" says Baross, whos been on a 20-year quest to find just such a microbe. Archaea are single-celled organisms that live under extreme environmental conditions, such as the high temperatures and crushing pressures below the seafloor. If heat-loving archaea were the first life on the planet, they would have needed a usable source of nitrogen, Baross says.
Known as FS406-22 because of the fluid and culture samples it came from, the archaeon discovered by the UW researchers is the first from a deep-sea hydrothermal vent that can fix nitrogen, says Mehta, first author on the Science paper.
It was collected at Axial Volcano on the Juan de Fuca Ridge off the coast of Washington and Oregon. Fixing nitrogen at 92 C smashes the previous record by 28 C, a record held by Methanothermococcus thermolithotrophicus, an archaeon that was isolated from geothermally heated sand ne
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Contact: Sandra Hines
shines@u.washington.edu
206-543-2580
University of Washington
14-Dec-2006