For plants and bacteria to form a symbiotic relationship, they have to communicate through chemical messaging that allows some bacteria to sense and move toward plants in the soil.

Birgit Scharf, an associate professor at Virginia Tech, recently received a $991,204 grant from the National Science Foundation (NSF) to study this plant-bacteria communication. The outcome of her work could result in less fertilizer applied to plants and higher crop yields.

“There will be direct benefits to farmers and the environment. Farmers would be able to use less artificial fertilizers, reducing cost and benefitting aquatic ecosystems through reduced influx of artificial fertilizers,” said Scharf, an associate professor of biological sciences in the College of Science and a Fralin Life Science Institute affiliate.

Her work will focus on characterizing the process of how Sinorhizobium meliloti (S. meliloti), a nitrogen-fixing bacterium, locates and forms a symbiotic relationship with the crop legume alfalfa.

Alfalfa is the fourth-most widely grown plant in the U.S. and a major food component for cattle. S. meliloti are often found living with the healthiest alfalfa plants in a beneficial symbiosis.

Scharf is interested in how these bacteria, which originate in soil, sense alfalfa and move in the soil to the plant's roots by a process known as chemotaxis. Using genetic and biotechnological approaches, she has pinpointed certain chemicals released by the plant, called betaines, that attract the bacteria.  She discovered that the bacteria use the sense of smell, or chemoreceptors, to locate the betaines exuded by the plant’s germinating seeds and roots.

With this grant, Scharf plans to further characterize these chemoreceptors, elucidate molecular mechanisms in S. meliloti, and expand the understanding of plant-bacteria communication. Scharf can use biotechnological approaches to create bacteria with improved chemoreceptors, which would strengthen the efficiency of the symbiosis and the health of the alfalfa plant.

The review panel for the NSF said, “Scharf’s research is potentially transformative, and we may gain new insights into the relationship between nitrogen fixing bacteria and plants, which would have broad implications to agriculture. This work provides easily identifiable applications to sustainability efforts for improved fertilizer use that could be used within the developing world.”

Scharf’s research on the S. meliloti and alfalfa symbiosis has far-reaching implications for world agriculture. A similar type of bacterial symbiosis is found in other legumes, such as soybeans, beans, and peas. Her research could be used to improve these plant-bacteria systems and increase crop yields.

Scharf received this grant in collaboration with Richard Helm, an associate professor of biochemistry in the College of Agriculture and Life Sciences, and Florian Schubot, an associate professor of biological sciences in the College of Science.

The grant was jointly funded from the NSF divisions of Molecular and Cellular Biosciences and Integrative Organismal Systems,  and the "Rules of Life" program, one of the NSF's 10 Big Ideas.

Scharf is currently serving on the scientific advisory board for the company Concentric, which produces biological optimizers; she may collaborate with them in the future to test how her research can improve crop yields and reduce the use of chemical fertilizers. 

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