Faculty Advisor

Dr. Silvia Rossbach


Biological Sciences

Presentation Date


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Atmospheric nitrogen fixation can be accomplished by free living microorganisms or by symbiosis between legume plants and rhizobia. The symbiosis between the alfalfa plant and Sinorhizobium meliloti is one example of the symbiotic relationship between legume plants and rhizobia. During the symbiosis, the rhizobia fix nitrogen for the plant and the plant in return provides carbohydrates for the bacteria. In order to maximize the plant’s yield in agriculture, recent technologies used include seed inoculants. Seed inoculation methods rely on coating the seeds with plant-growth promoting bacteria. Besides nitrogen-fixing bacteria, the seeds may also be coated with microorganisms aiding in mineral solubilization, biological control or nutritional requirements. The goal of this study was to identify the different bacteria present in coated alfalfa seeds and their impact on alfalfa plant yield. Bacteria were isolated from the coated seeds and purified. Several morphologically different bacteria were isolated from the coated seeds. Their 16S rRNA genes were amplified and sequenced. Several Bacillus spp. were identified. Surprisingly, no rhizobial strains were found among the isolated strains. Nevertheless, we performed a plant inoculation assay with the coated seeds and nodules were observed, suggesting the presence of rhizobia in the inoculants. We also screened for the presence of nitrogen fixation (nifH) genes in the bacterial isolates. The results indicated that two strains contained the nifH genes. Another plant inoculation assay with uncoated alfalfa seeds is under investigation in order to evaluate the impact of each isolated strain on alfalfa growth.