All living things require nitrogen for building many important molecules, including DNA, RNA, and proteins. Animals get their nitrogen through other animals and, ultimately, through plants. However, even though the atmosphere is 78-percent nitrogen, it is too stable for plants to use directly. It must be “fixed.” Non-leguminous plants depend on nitrogen that has built up in the soil by leguminous plants, through other less dependable processes, or through nitrogen fertilizer. The more enterprising legumes get their nitrogen through a symbiotic relationship with bacteria called rhizobia.
The rhizobia split the paired nitrogen molecules, then convert each to ammonia, which is more chemically reactive and thus usable to plants.
Understanding this beneficial relationship is the research focus in the laboratory of Michael Kahn, a professor in Washington State University’s School of Molecular Biosciences, Center for Integrated Biotechnology, and Institute of Biological Chemistry.
Kahn and his team have nearly completed a monumental step in understanding nitrogen fixation. Under the direction of his postdoctoral assistant, Brenda Schroeder, graduate and undergraduate WSU students have cloned over 6,000 of one nitrogen-fixing bacterium’s genes in less than one year. This means they’ve made copies of each gene that codes for proteins, isolated the gene copies, and put each into its own small piece of DNA, creating a library of all the genes in the species S. meleloti. Scientists can now use the gene library to begin identifying exactly what each fragment does. “The premise of the project was to share the clones and send out copies for further research,” says Schroeder. “With this library, researchers can work with the whole genome and figure out which genes are turned on under what circumstances.”
Their work adds a “predictive” aspect to DNA sequencing, according to Schroeder. When scientists find the DNA sequence of an organism’s entire genome, as they have for humans and fruit flies, they usually don’t know what most of it means. Kahn’s lab has taken the first step in putting biological meaning to the nitrogen-fixing bacteria’s DNA sequence.
“I can’t say enough about the dedication, hard work, and diligence of the team,” says Schroeder. The achievement stands out. For example, the genes of the intensively-studied bacteria E. coli have not been entirely cloned.
At this point, the research findings and applications stemming from the creation of this gene library can only be imagined. Perhaps scientists could identify the group of genes that convert free nitrogen into fixed nitrogen, and then put extra copies of those genes into new bacteria. The new bacteria could be introduced to soil in lieu of fertilizer, not only increasing the size of your tomatoes, but perhaps also helping to ensure the world’s food supply.