CAREER: Novel Determinants of Motility and Chemotaxis in Sinorhizobium meliloti

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Nitrogen is the most limiting nutrient for plant growth. While chemically synthesized inorganic nitrogen fertilizers are effective in increasing crop yields, they are costly and also have a negative impact on the environment, especially on aquatic ecosystems. In contrast, sustainable agriculture relies on biological nitrogen fixation as an economically attractive and ecologically viable source of new nitrogen. The conversion of molecular nitrogen into ammonia is performed by bacteria (Rhizobia) that live in symbiosis with leguminous plants such as peas, soy beans, and alfalfa. The research will be carried out using the symbiotic model system, the nitrogen-fixing soil bacterium Sinorhizobium meliloti (S. meliloti). The process of chemotaxis enables motile rhizobia to preferentially move in the soil towards host plant roots and supports efficient interaction between symbiosis partners. Many motile bacteria are propelled by means of rotating flagella, driven by a powerful, self-assembling nanomachine. The unique flagellar motor and the specially adapted chemotaxis system of S. meliloti make cells more efficient at maneuvering in the viscous soil environment, leading to better survival and optimal interaction with their host plant alfalfa. Previous research uncovered several novel molecular mechanisms governing chemotactic responses and motility in S. meliloti, thereby setting the stage for an in-depth analysis of the underlying molecular events. The overarching goal of this project is to analyze the specific adaptations that occurred in S. meliloti motility and chemotaxis due to the soil habitat and communication with its plant host. The first objective of the research analyzes the roles of two novel proteins in the response of S. meliloti to quickly changing environmental signals, which is essential for bacterial survival. The second objective determines the cellular concentrations and enzymatic activities of key chemotaxis components, allowing prediction of bacterial behavior in the interaction with alfalfa crop. The third objective will identify the function of newly discovered flagellar motor components in facilitating effective movement of S. meliloti in the soil and towards symbiosis partners. This research will lead to the discovery of significant bacterial properties and impact current understanding of how bacterial symbionts respond to plant signals and efficiently move through soil. Broader Impacts The project directly benefits future agricultural and environmental issues for society. By enhancing understanding of the cues that bacterial symbionts use to efficiently interact with their host crop, the research will impact biological nitrogen fixation and thus crop yields and reduce the use of detrimental synthetic fertilizers. The project will also vertically integrate research activities with educational activities through the development of an undergraduate classroom exercise addressing currently open research questions, which will transform into scientific discoveries in the research laboratory. The existing, successful outreach program of the Microbiology Club of Virginia Tech will be expanded to rural, underdeveloped communities of Appalachia. Outreach activities in the form of interactive lectures and hands-on activities will promote scientific awareness across the educational spectrum, including a local 4-H Agricultural Club and rural elementary schools. Studies of motility and chemotaxis can be demonstrated easily and will allow the development of innovative, inquiry-based microbiology lessons with High School science teachers, a valuable strategy for effective learning. Collaboration with Novozymes? BioAgricultural Group will give Virginia Tech students the opportunity not only to experience basic research approaches at the university and applied research in industry through merged collaborative training programs, but also to increase their chances for recruitment into professional careers. Overall, this project integrates research and education through the fusion of classroom and laboratory research, hands-on outreach activities in rural communities, and internships in industry, which will promote student engagement and transform student learning and will permanently stimulate student's interest in science.