Enrichment and Isolation of Rhizobium

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Summary

This project attempted to enrich and isolate Rhizobium, a natural nitrogen-fixating soil bacteria, from root nodules on legumes. Rhizobium is an important microorganism for the environment because it is involved in a symbiotic relationship with plants (mainly legumes), converting nitrous gas in the air to ammonia, which can further be fixated into a form of nitrogen that plants can use. Using results from our soybean nodule sample, we were partially successful in isolating Rhizobium on clover root nodules. We overcame the obstacle of preparing bacteria from small root nodules and our media supported the growth of both of our samples successfully. Our organism was round and mucilaginous macroscopically, which might explain why our Gram stains and capsule stains showed non-cellular globules in the background. We believe our organism could be a species of Rhizobium, since it grew fast, was Gram negative, underwent aerobic respiration, was catalse positive, motile, and utilized dextrose and mannitol. The only feature of our organism that was not concurring with the soybean sample results was that our organism's colonies were yellowish while the soybean BradyRhizobium colonies were white. We can confirm our clover bacteria sample results with the BradyRhizobium results because BradyRhizobium has almost exactly the same characterisitcs as a typical species in the Rhizobium genus. The yellow colonies may suggest that we could possibly have isolated not Rhizobium, but Azotobacter, also a soil bacteria involved with nitrogen fixation. Azotobacter shares many of the same characteristics as Rhizobium. However, our enrichment protocol was successful for the isolation of rhizobiod bacteria found on the soybean nodule.