A genetic analysis of soil samples indicates that a group of microorganisms called crenarchaeota are the Earth's most abundant land-based creatures that oxidize ammonia, according to an international team of researchers from Norway, Germany, United Kingdom and the United States.

Soil microbes, in a process known as nitrification, combine ammonia with oxygen to form nitrates, which are used as nutrients by plants.

"Ammonia oxidation is an important step in the nitrogen cycle that was believed for the last 100 years to be solely performed by bacteria," says Christa Schleper, full professor of Molecular biology of Archaea at University Bergen, Norway.

The discovery was made possible by a combination of different techniques ranging from molecular biology, biochemistry to metagenomics. Using a novel sequencing technique and bioinformatics tools, Stephan C. Schuster, associate professor of biochemistry and molecular biology at Penn State, and his co-workers accurately measured the quantities of active bacteria and archaea in the complex mixtures of soil organisms. The international research team reports their findings in today's (Aug. 17) issue of Nature.

Archaea are single-celled microbes that, along with bacteria, comprise a category of small organisms whose genetic material, or DNA, is not stored in a nucleus (as it is in animals and plants). Crenarchaeota, which belong to the archaea, are found in various habitats, including soil.

"We think crenarchaeota in soil gain their energy from oxidizing ammonia," said Schuster. "But we don't know yet if they can also gain energy by other means. The bacterial counterparts can only do ammonia (and urea) oxidation, nothing else."

During a recent study of a collection of genes in microorganisms, researchers had stumbled on a particular gene, which is responsible for the production of a key enzyme used for the oxidation of ammonia.

The gene was subsequently found in a m
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Contact: Amitabh Avasthi
aem1@psu.edu
814-865-9481
Penn State
16-Aug-2006