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Rhizobium and Other N-fixing Symbioses

  1. Kristina Lindström,
  2. Seyed Abdollah Mousavi

Published Online: 15 NOV 2010

DOI: 10.1002/9780470015902.a0021157



How to Cite

Lindström, K. and Mousavi, S. A. 2010. Rhizobium and Other N-fixing Symbioses. eLS. .

Author Information

  1. University of Helsinki, Helsinki, Finland

Publication History

  1. Published Online: 15 NOV 2010


Nitrogen-fixing symbioses between bacteria and plants are major nitrogen contributors to the terrestrial biosphere. The Rhizobium–legume interaction is the best known and is agronomically the most important one. Several alpha- and betaproteobacterial species (rhizobia) can infect legume roots via root hair or crack invasion, preceded by signal exchange in the rhizosphere and followed by signal transduction in the root, resulting in the construction of a nitrogen-fixing root nodule. Actinorhizal nodule formation by members of the actinobacterial genus Frankia follows the same pattern but is less known in detail. The nitrogen-fixing root symbioses have the same evolutionary origin as mycorrhizal symbioses. Cyanobacterial nitrogen-fixing symbioses are more diversified and formed mainly with representatives of genus Nostoc, and occur in diverse plant groups, the best known being Azolla, Cycas and Gunnera. Whole-genome sequencing of the microbial symbionts has revealed interesting features related to the genetics of signalling, genome architecture and biogeography.

Key Concepts:

  • Symbiotic nitrogen fixation in plants contributes significantly to terrestrial ecosystems and sustainable agriculture.

  • Symbiotic nitrogen-fixing interactions arose several times during evolution.

  • The Rhizobium–legume symbiosis serves as a model and paradigm for other symbiotic interactions between bacteria and plants.

  • Nitrogen-fixing root symbioses have an origin common with mycorrhizal symbioses.

  • Most rhizobia have well-conserved nodulation genes which encode signals, nodulation factors, which are perceived by the plant.

  • Cyanobacterial symbioses with plants are diversified, but involve mainly one microbial genus, Nostoc.


  • symbiosis;
  • nitrogen fixation;
  • plant–microbe interaction;
  • Rhizobium;
  • Frankia;
  • cyanobacteria;
  • infection;
  • evolution;
  • signalling;
  • genomes