Post symbiotic analysis of the Bradyrhizobium japonicum-soybean symbiosis: proteomics and mutagenesis of protocatechuate 3, 4-dioxygenase paralogs
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Symbiotic nitrogen fixation between Bradyrhizobium japonicum and soybean is the predominant pathway by which the abundant, inert supply of atmospheric dinitrogen is made available in the form of reduced nitrogen, the most limiting nutrient in agricultural production. In a microaerobic environment huge amounts of energy are required to fuel this process and a steady supply of carbon substrates is needed from the symbiotic legume partner to fuel nitrogenase. The extension of the duration of nitrogen fixation could lead to greater agricultural production. In order to better understand the metabolism of B. japonicum bacteroids past peak nitrogen fixation proteomics, including cellular compartments, was done over 119 days. A metabolic pathway of interest, β-ketoadipate pathway, was analyzed for symbiotic phenotype by mutating both sets of genes encoding pcaHG. Finally to better understand if the bacteroids of B. japonicum were dedifferentiating into their free-living form, scanning and transmission electron micrographs were taken of post-peak nitrogen fixing soybean nodules with the discovery of appendages being created by B. japonicum in the post-symbiotic state.