Birgit Scharf, assistant professor of biological sciences in the College of Science at Virginia Tech, is interested in making plants grow and in finding a way to do it without environmentally-disastrous chemically-synthesized inorganic nitrogen fertilizers.

To that end, Scharf, also an affiliate of the university's Fralin Life Science Institute, has received approximately $900,000 through a National Science Foundation CAREER Award to analyze the role of proteins within Sinorhizobium meliloti (S. meliloti), a nitrogen-fixing bacterium that forms a symbiotic relationship with the important crop legume, alfalfa. 

In soil, the bacteria move toward plant roots, invade the host plant, and provide nitrogen to plants for growth.

“We have three objectives we’ve been working on,” said Scharf. “First we have been analyzing how two novel proteins allow S. meliloti to respond to quickly-changing environmental signals, which is essential to survival. Then we want to determine the activities of chemotaxis components – what makes the bacterium move to the host plant – to help us predict its behavior during crop interaction. Finally, we want to identify how its flagellar motor works, which will impact our understanding of how bacterial symbionts respond to plant signals and effectively move through the soil.”

Scharf found that S. meliloti is attracted to particular amino acids that are exuded by the roots of host plants. 

The research team then identified the bacterial chemotaxis protein that senses proline and other amino acids and determined how the attractant response is transmitted to the flagellar motor. 

Her research group also discovered that another group of chemicals exuded by the host plant, betaines, serve to attract these beneficial bacteria. Betaines protect plants against environmental stress, but their role in communication with bacteria is a new discovery. 

The team is now exploring how betaines bind to bacterial receptor proteins to better understand this previously-unknown signaling system.

“Working with a group at Rutgers University, we are looking into the structure of one of the novel proteins that will help us understand its interaction with partner proteins and its function in signaling termination,” Scharf said.

By increasing the understanding of the cues bacterial symbionts use to interact with host crops, Scharf’s work will provide a new angle to long-standing, but as-yet largely ineffective efforts to enhance nitrogen fixation to help increase crop yields and to reduce the use of synthetic fertilizers that have an especially negative impact on aquatic ecosystems.

Scharf joined Virginia Tech in 2008, and has published more than 40 research papers. She received her doctoral degree from the Max-Planck Institute of Molecular Physiology in Germany and has held post-doctoral fellowships at the Max-Planck Institute, Harvard University, and the University of Regensburg (Germany). She held an independent group leader position at the University of Regensburg from 2000 to 2007.

Scharf is co-advising the Undergraduate Microbiology Club and with the club, was honored with a College of Science Outreach Excellence Award in 2013. The club offers hands-on microbiology-related workstations and no-cost supplies to local elementary schools and participates in annual science fairs including Kids’ Tech with booths designed to educate visitors about microbiology.



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