Genetic, Biochemical, and Physiological Characterization of the Plant Symbionts Sinorhizobium meliloti and Rhizobium leguminosarum

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Rhizobium is a Gram-negative soil bacterium that interacts with legumes to produce nitrogen fixing nodules on the roots thus allowing the plant to live under nitrogen deficient regimes. The genome of Sinorhizobium meliloti is sequenced and has been adopted as a model bacterium in which to study plant-microbe interactions. Although the genetics and biochemistry of the signaling involved during early nodulation are rapidly progressing, comparatively little is understood about how metabolism affects these early stages of plant-bacteria interaction. The inability to utilize sugars that are commonly found around the roots of legume plants can affect how the rhizobia interact with the plant. Strains that are affected in metabolism, and are either unable to compete for nodule occupancy or are unable to form effective nitrogen fixing symbiosis will be used as genetic tools to identify determinants that are necessary for efficient associations. The genes involved in these processes will be characterized physiologically, genetically as well as biochemically to identify how they affect the symbiosis, both at a whole plant level, as well as at a molecular level. The study of rhizobia is of particular interest to those working in the agriculture, specifically in plant-microbe interactions, however, as rhizobia have commonalities with many other bacteria this work on metabolism can extend to a broader scientific community working on problems such as bioremediation, drug development or other applications. In addition, the knowledge generated also has the potential to be translational, and have applicability to Canada's inoculum industry. The ability to produce better inoculums for legume production will greatly decrease the nitrogen input needed for agriculture and lead to more sustainable agricultural practices.