Bacteria that fix nitrogen from the atmosphere
Rhizobia are bacteria that live in association with the roots of legumes (pulses) in a symbiotic relatoinship.
Rhizobia are able to take nitrogen from the atmosphere and bind it into a soluble form that plants can use. Nitrogen deficiency is a common problem for plants, which is addressed by huge inputs of fertiliser. Rhizobia enable legumes to be grown commercially without nitrogen fertiliser. Legumes are often planted as intercrops to enhance soil nitrogen levels.
Rhizobia's ability to fix nitrogen has attracted attention for possibilities with genetic engineering. Giving crops besides legumes the ability to fix nitrogen would have huge benefits for agriculture. The relationships between legumes and rhizobia, however, are very complex and are governed by many genes. This has made it impossible thus far to to transfer the rhizobia symbiosis to other plants.