Editing Symbiosis (section)

=== Nitrogen fixation in legumes ===

{{further|Rhizobia}}

[[File:Soybean-root-nodules (cropped).jpg|thumb|upright=1.1|[[Root nodule]]s, each containing billions of ''[[Rhizobiaceae]]'' bacteria, fix nitrogen in symbiosis with a [[legume]]. ]]

'''Rhizobia''' are [[bacteria]] that [[Nitrogen fixation|fix nitrogen]] inside the [[root nodule]]s of [[legume]]s such as [[bean]]s and [[clover]]. To express genes for nitrogen fixation, rhizobia require a plant [[Host (biology)|host]]; they cannot independently fix nitrogen.<ref name="Zahran1999">{{Cite journal |last=Zahran |first=Hamdi Hussein |date=1999-12-01 |title=Rhizobium-legume symbiosis and nitrogen fixation under severe conditions and in an arid climate |journal=Microbiology and Molecular Biology Reviews |volume=63 |issue=4 |pages=968–989, table of contents |doi=10.1128/MMBR.63.4.968-989.1999 |pmc=98982 |pmid=10585971}}</ref> 
Rhizobia infect the legume's roots and produce nodules where they fix nitrogen gas (N<sub>2</sub>) from the atmosphere, turning it into a more readily useful form of nitrogen. From here, the nitrogen is exported and used for growth in the legume.<ref name="Herridge2013">{{cite journal |last=Herridge |first=David |title=Rhizobial Inoculants |journal=GRDC |date=2013}}</ref>