Contact: Michael Kahn, Professor, School of Molecular Biosciences, 509-335-8327, kahn@wsu.edu
A Library of Rhizobial Genes
Postdoctoral assistant Brenda Schroeder and Professor Michael Kahn in a nitrogen-producing pea field.
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.