Lifestyle alternatives for rhizobia: Mutualism, parasitism, and forgoing symbiosis

R. Ford Denison, E. Toby Kiers

Research output: Contribution to journalShort surveypeer-review

154 Scopus citations


Strains of rhizobia within a single species can have three different genetically determined strategies. Mutualistic rhizobia provide their legume hosts with nitrogen. Parasitic rhizobia infect legumes, but fix little or no nitrogen. Nonsymbiotic strains are unable to infect legumes at all. Why have rhizobium strains with one of these three strategies not displaced the others? A symbiotic (mutualistic or parasitic) rhizobium that succeeds in founding a nodule may produce many millions of descendants. The chances of success can be so low, however, that nonsymbiotic rhizobia can have greater reproductive success. Legume sanctions against nodules that fix little or no nitrogen favor more mutualistic strains, but parasitic strains that use plant resources only for their own reproduction may do well when they share nodules with mutualistic strains.

Original languageEnglish (US)
Pages (from-to)187-193
Number of pages7
JournalFEMS Microbiology Letters
Issue number2
StatePublished - Aug 15 2004
Externally publishedYes

Bibliographical note

Funding Information:
Our research on this topic is supported by an NSF Graduate Fellowship, NSF grant 0212674, the Kearney Foundation of Soil Science, and the Land Institute.


  • Evolution
  • Ineffective
  • Mutualism
  • Nitrogen-fixation
  • Parasitism
  • Rhizobium
  • Sanction
  • Symbiosis


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