• L Moulin, A Munive, B Dreyfus, and C Boivin-Masson.
• Laboratoire des Symbioses Tropicales et Méditerranéennes, IRD-INRA-CIRAD-ENSAM Baillarguet, Montpellier, France.
• Nature. 2001 Jun 21;411(6840):948-50.

AbstractMembers of the Leguminosae form the largest plant family on Earth, with around 18,000 species. The success of legumes can largely be attributed to their ability to form a nitrogen-fixing symbiosis with specific bacteria known as rhizobia, manifested by the development of nodules on the plant roots in which the bacteria fix atmospheric nitrogen, a major contributor to the global nitrogen cycle. Rhizobia described so far belong exclusively to the alpha-subclass of Proteobacteria, where they are distributed in four distinct phylogenetic branches. Although nitrogen-fixing bacteria exist in other proteobacterial subclasses, for example Herbaspirillum and Azoarcus from the phylogenetically distant beta-subclass, none has been found to harbour the nod genes essential for establishing rhizobial symbiosis. Here we report the identification of proteobacteria from the beta-subclass that nodulate legumes. This finding shows that the ability to establish a symbiosis with legumes is more widespread in bacteria than anticipated to date.

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