Bradyrhizobium japonicum
Brandon Basler

Bradyrhizobium japonicum is a rod-shaped, Gram-negative, mesophilic, chemohetertrophic, nitrogen fixing bacteria found in the roots of a soybean plant, Glycine maxBradyrhizobium japonicum has domain of Bacteria and phylum of Proteobacteria.  It has class Alphaproteobacteria, order Rhizobiales, and is part of the family Bradyrhizobiaceae.  Bradyrhizobium japonicum is not pathogenic, but is found in that soil in which the plant is planted and then infects the plant.  Bradyrhizobium japonicum forms a symbiotic, nitrogen fixing relationship with the soybean plant just like many Rhizobia do with legumes.  Bradyrhizobium japonicum is found in the root region of the soybean where it forms nodules and fixes nitrogen into a useable form for the soybean plant.  This relationship is very agriculturally important because it drastically reduces the amount of nitrogen fertilizers needed to grow the soybeans if these bacteria were not present.  The main research involving Bradyrhizobium japonicum is USDA 110 strain genome project, in which the complete genome of this strain was documented.

Bradyrhizobium japonicum forms symbiotic, nitrogen fixing relationship with the soybean plant.  Nitrogen fixation means that Bradyrhizobium japonicum converts N2 gas, the most abundant gas in the air we breathe and unusable to plants, into Ammonia (NH3), which is the most common source of nitrogen for most plants.  This relationship benefits both bacteria and the plant.  The soybean receives the fixed nitrogen in return for giving the bacteria energy and protection.  The bacterium lives in the roots of the soybean where it forms nodules, small growths on the roots.  Here the bacteria fixed the nitrogen so the plant can absorb it as soon as it is converted.  In addition, the nodules give the bacteria protection from the elements.  Soybeans may have several hundred nodules at once that are short live and constantly being replaced by others.  In the formation of the nodules the bacteria and the soybean work together.  Proteins in the membrane of the bacteria attach to the root of the plant and send the root signals that it is present.  The nodules form around the bacteria about a week after the bacteria has infected the root area. As the plant gives the bacteria energy, the bacteria gives the plant fixed nitrogen.  In addition the growth of the nodules and bacteria is directly related to the growing state of the plant.  When the plant is thriving, so do the nodules.  Likewise, when the plant is not in the best of health the nodules also suffer.  Even during the time of seed production the nodules start to fade as the plant puts most of its energy into the formation of the seed.  In a crop setting this way of nitrogen fixation almost 400 pounds of nitrogen per acre per year can be transformed into usable form thanks to these bacteria.

This ability to be so effective at nitrogen fixation prompted the research of the genome of these bacteria.  The strain of Bradyrhizobium japonicum USDA 110 that was used in the genome project was first isolated in 1959 in Florida because it was superior in this nitrogen fixation.  The project completely sequenced the genome of the bacteria.  In addition some genes that controlled nitrogen fixation and nodule formation were isolated.  These genes are now being introduced to other bacterium and even some plants.


Kosslak, Renee, Roger Bookland, John Barkei, Herbert E. Paaren, Edward R. Appelbaum. "Induction of Bradyrhizobium japonicum common nod genes by isoflavones isolated from Glycine max." PNAS 84(1987)

Sanjuan, J, R W Carlson, H P Spaink, U R Bhat, W M Barbour, J Glushka, G Stacey. "A 2-O-methylfucose moiety is present in the lipo-oligosaccharide nodulation signal of Bradyrhizobium japonicum." PNAS 89(1992)

Lindemann, W.C., C.R. Glover. "Nitrogen Fixation." Cooperative Extension Service 129(2003): 4.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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