Amanda Plein

Document Type

Honors Thesis


Bradyrhizobium japonicum is a nitrogen-fixing bacterium that forms a symbiotic relationship with legumes such as soybeans. The bacterium plays an important role in providing the soybean plant with usable nitrogen while it receives photosynthetic products in return. B. japonicum strain USDA110 can utilize phytohormone indole-3-acetic acid (IAA) as an energy source. It has been found that the iorA gene is up-regulated in response to IAA. A mutant strain of the bacterium, ∆iorA, had the iorA gene removed in a previous experiment. To further investigate the role of IAA and its effects on B. japonicum, both the wild-type and mutant strains were exposed to varying concentrations of IAA. The results show that the iorA gene allows for growth in IAA treatment conditions, but the growth was reduced in comparison to glycerol treatments. This suggests the iorA gene may provide an evolutionary advantage by allowing energy to be obtained from alternate carbon sources.

Publication Date






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