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 of legumes 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. The inability to utilize rhamnose, a constituent of the plant cell wall, yields a strain that is uncompetitive for nodule occupancy, whereas a strain unable to use galactose gives rise to a strain that is more competitive for nodule occupancy. This research proposal will address the role the catabolism of these compounds plays during the symbiotic development. The genes involved in these processes will be characterized genetically and biochemically. In addition, direct confocal imaging will assess how each of these strains behaves symbiotically. The fundamental knowledge that will be generated from the proposed work will be relevant both to the scientific community as well as to Canadians generally if these technologies can be utilized to produce better inoculums for legume production.