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Getting the fix on Nitrogen

Nitrogen is an essential nutrient for plant growth, but not all forms of nitrogen are usable by plants. Although Earth’s atmosphere is rich in nitrogen, the inert atmospheric gas is useless to most organisms.
Some plants, though, form symbiotic relationships with bacteria called rhizobia. In a complicated exchange of nutrients, rhizobia produce an abundance of nitrogen, making it available to the plant. Legumes, such as such as alfalfa, soybeans, chickpeas and lentils, are especially good at fixing nitrogen. Grown as cover crops in order to enrich soil, legumes are typically higher in protein than other crop plants, probably due to their symbiosis with nitrogen-fixing bacteria.

Michael Kahn,
professor in WSU’s Institute of Biological Chemistry and the School of Molecular Biosciences, is a member of a team that sequenced the genome of a rhizobia bacterium that infects alfalfa roots. Along with a collaborator at Stanford University, he led an effort to clone and manipulate all 6,200 genes predicted to be in that sequence. To bring down the cost per gene far enough to make it interesting to funding agencies, Kahn’s lab has developed several new genetic-research techniques. Kahn and his team are investigating the function of each gene and how each gene contributes to the bacteria’s ability to persist in the soil, infect alfalfa roots, and lead to a productive, nitrogen-fixing symbiosis.
Investigators hope their research will improve the efficiency of nitrogen fixation, make establishment of the symbiosis more reliable under different growing conditions, and extend the host range of nitrogen-fixing symbiotic relationships. Legumes are often used as a green manure, and the nitrogen they accumulate can be used by subsequent crops grown in rotation. Research into the legume-rhizobia relationship will lead to improved yield, elimination of a major fertilizer input, and improved designs for sustainable agriculture.
For more information on Kahn’s research, please visit:

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