An international research team has decoded the genome of an important microbe that provides an essential source of nitrogen for plants, people and other living organisms on Earth. Researchers say that the new genome map could provide the foundation for improving crop yields, while reducing the use of nitrogen-based fertilizers by farmers.

Scientists from Stanford and seven European and Canadian institutions began sequencing the DNA of the bacterium, Sinorhizobium meliloti, in 1998. Their results a complete map of the S. meliloti genome appear in the July 27 issue of the journal Science.

S. meliloti is one of several bacterial species with the remarkable ability to transform atmospheric nitrogen into other chemicals a process called nitrogen fixation. All living things need nitrogen a basic ingredient of proteins, DNA and other organic molecules. But obtaining usable nitrogen from nature is a complicated process, despite its abundance: Nearly 80 percent of the atmosphere consists of nitrogen gas, which unlike oxygen cannot be absorbed by most living organisms. Nitrogen-fixing bacteria in the ground chemically convert atmospheric nitrogen into ammonia a nitrogen-based compound that plants can use to produce proteins. Animals and people, in turn, obtain nitrogen by consuming protein from plants and herbivorous animals.

"Nitrogen fixation is essential to life on Earth. Without it, there would be no proteins, for example," says Sharon R. Long, the William C. Steere, Jr. Pfizer Inc. Professor of Biological Sciences at Stanford and a lead co-author of the Science study.

"All nitrogen fixation is carried out by bacteria," she adds. "The specific attraction of studying the S. meliloti bacterium is the symbiosis."

S. meliloti is one of several symbiotic nitrogen-fixing bacteria known as Rhizobia that live in the roots of legumes a major plant family that includes peas, beans, soybeans, peanuts, alfalfa an
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
26-Jul-2001