Have you ever bitten into a nice legume and thought "wow, this is delicious"?  If so, you have Rhizobia to thank.  Without the symbiotic relationship between legumes and Rhizobia, we would be at a loss for tasty legumes!  Legumes are plants that make seeds in a pod.  Some popular legumes include peas, soybeans, beans, alfalfa, and clover (Long).  Without Rhizobia legumes would not be able to grow and soil would not be as rich with nitrates.

Even the early Greeks knew that soil which had recently grown beans was better for crops.  The real discovery of Rhizobia was in 1886 by German Agricultural chemists Hermann Hellriegel and Hermann Willfarth.  They noted it as the bacteria that fixes nitrogen.  (Tallack)

The real magic of Rhizobia is that is it able to turn free nitrogen (N₂) from the air, into compounds that have ammonium (NH⁺), nitrite (NO₂^-), and nitrate (NO₃^-).  This is called nitrification or nitrogen fixing.  The Rhizobium form nodules on  legume roots to help convert diatomic nitrogen gas to ammonia. (atmosphere)

• Rhizobia are primarily aerobic, meaning they need oxygen, but some can function with less oxygen (Long).

• They are rod shaped and use flagella to move (Long). 

• They are gram negative when gram stained (Long).  

• They do not form spores but rather reproduces asexually in nodules formed on roots (Long). 

• Because of their symbiotic relationship with legumes, rhizobia receive all of their nutrition chemoautotrophically, meaning the plants provide them with energy and carbon-based molecules (Tallack).

• They live mostly in the soil at about 25-30 degrees Celsius (Long). 

Fun Facts:

• Each year, rhizobia produce about 200 million tons of fixed nitrogen (Tallack).
• The word rhizobia originated from the Greek words Riza, which means Root, and Bios, which means Life (What Is Rhizobia?).

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[1]"Taxonomy Browser." NCBI. National Center for Biotechnology Information. 16 Dec. 2007 <http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Undef&id=379&lvl=3&lin=f&keep=1&srchmode=1&unlock>.