, Volume 55, Issue 2, pp 85–90 | Cite as

Measuring the fitness of symbiotic rhizobia

  • William C. RatcliffEmail author
  • Kyra Underbakke
  • R. Ford Denison


The legume-rhizobia symbiosis is an important model system for research on the evolution of cooperation and conflict. A key strength of this system is that the fitness consequences of greater or lesser investment in cooperative behaviors can be measured for each partner. Most empirical studies have characterized the fitness of symbiotic rhizobia exclusively by their numbers within nodules, often estimated using nodule size as a proxy. Here we show that the relationship between nodule size and rhizobial numbers can differ drastically between strains of the same species. We further show that differences in accumulation of the storage polyester poly-3-hydroxybutyrate (PHB), which can support future reproduction, can be large enough that even direct measurements of rhizobial numbers alone can lead to qualitatively incorrect conclusions. Both results come from a comparison of strains differing in production of the ethylene-inhibitor rhizobitoxine (Rtx). A broader study (using three legume-rhizobia species pairs) showed that PHB/cell cannot be reliably estimated from its correlation with rhizobia/nodule or nodule size. Differences in PHB between strains or treatments will not always make major contributions to differences in fitness, but situation-specific data are needed before PHB can safely be neglected.


Cooperation Symbiosis Evolutionary stability Cheating Poly-β-hydroxybutyrate Rhizobitoxine Offspring quality 



This work was supported by NSF grant DEB-0918897.


  1. Bergersen FJ, Gibson AC, Licis I (1995) Growth and N2-fixation of soybeans inoculated with strains of bradyrhizobium japonicum differing in energetic efficiency and PHB utilization. Soil Biol Biochem 27:611–616CrossRefGoogle Scholar
  2. Denison RF, Kiers ET (2011) Life histories of symbiotic rhizobia and mycorrhizal fungi. Curr Biol 21:R775–R785PubMedCrossRefGoogle Scholar
  3. Duodu S, Bhuvaneswari TV, Stokkermans TJW, Peters NK (1999) A positive role for rhizobotoxine in Rhizobium-legume symbiosis. Mol Plant Microbe Interact 12:1082–1089CrossRefGoogle Scholar
  4. Gubry-Rangin C, Garcia M, Bena G (2010) Partner choice in medicago truncatula–Sinorhizobium symbiosis. Proc R Soc Lond B 277:1947–1951CrossRefGoogle Scholar
  5. Heath KD, Tiffin P (2007) Context dependence in the coevolution of plant and rhizobial mutualists. Proc R Soc Lond B 274:1905–1912CrossRefGoogle Scholar
  6. Henery ML, Westoby M (2001) Seed mass and seed nutrient content as predictors of seed output variation between species. Oikos 92:479–490CrossRefGoogle Scholar
  7. Kiers ET, Rousseau RA, West SA, Denison RF (2003) Host sanctions and the legume-rhizobium mutualism. Nature 425:78–81PubMedCrossRefGoogle Scholar
  8. Kiers ET, Hutton MG, Denison RF (2007) Human selection and the relaxation of legume defences against ineffective rhizobia. Proc R Soc Lond B 274:3119–3126CrossRefGoogle Scholar
  9. Law JH, Slepecky RA (1961) Assay of poly-ß-hydroxybutyric acid. J Bacteriol 82:33–36PubMedGoogle Scholar
  10. Mercan N (2002) Production of poly-b-hydroxybutyrate (PHB) by some rhizobium bacteira. Turk J Biol 26:215–219Google Scholar
  11. Moles AT, Westoby M (2004) Seedling survival and seed size: a synthesis of the literature. J Ecol 92:372–383CrossRefGoogle Scholar
  12. Okazaki S, Yuhashi KI, Minamisawa K (2003) Quantitative and time-course evaluation of nodulation competitiveness of rhizobitoxine-producing Bradyrhizobium elkanii. FEMS Microbiol Ecol 45:155–160PubMedCrossRefGoogle Scholar
  13. Oono R, Denison RF, Kiers ET (2009) Tansley review: controlling the reproductive fate of rhizobia: how universal are legume sanctions? New Phytol 183:967–979PubMedCrossRefGoogle Scholar
  14. Ratcliff WC, Denison RF (2009) Rhizobitoxine producers gain more poly-3-hydroxybutyrate in symbiosis than do competing rhizobia, but reduce plant growth. ISME J 3:870–872PubMedCrossRefGoogle Scholar
  15. Ratcliff WC, Kadam SV, Denison RF (2008) Polyhydroxybutyrate supports survival and reproduction in starving rhizobia. FEMS Microbiol Ecol 65:391–399PubMedCrossRefGoogle Scholar
  16. Riis V, Mai W (1988) Gas chromatographic determination of poly-beta-hydroxybutyric acid in microbial biomass after hydrochloric acid propanolysis. J Chromatogr A 445:285–289CrossRefGoogle Scholar
  17. Ruan X, Peters NK (1992) Isolation and characterization of rhizobitoxine mutants of bradyrhizobium japonicum. J Bacteriol 174:3467–3473PubMedGoogle Scholar
  18. Sachs JL, Ehinger MO, Simms EL (2010) Origins of cheating and loss of symbiosis in wild bradyrhizobium. J Evol Biol 23:1075–1089PubMedCrossRefGoogle Scholar
  19. Simms EL, Taylor DL, Povich J, Shefferson RP, Sachs JL, Urbina M, Tausczik Y (2006) An empirical test of partner choice mechanisms in a wild legume-rhizobium interaction. Proc R Soc Lond B 273:77–81CrossRefGoogle Scholar
  20. Sugawara M, Okazaki S, Nukui N, Ezura H, Mitsui H, Minamisawa K (2006) Rhizobitoxine modulates plant–microbe interactions by ethylene inhibition. Biotechnol Adv 24:382–388PubMedCrossRefGoogle Scholar
  21. Tavernier P, Portais J, Saucedo JEN, Courtois J, Courtois B & Barbotin JN (1997) Exopolysaccharide and poly-b-hydroxybutyrate coproduction in two rhizobium meliloti strains. Appl Environ Microbiol 63Google Scholar
  22. van Veen J, van Overbeek L, van Elsas J (1997) Fate and activity of microorganisms introduced into soil. Microbiol Mol Biol Rev 61:121–135PubMedGoogle Scholar
  23. West SA, Griffin AS, Gardner A (2007) Social semantics: altruism, cooperation, mutualism, strong reciprocity and group selection. J Evol Biol 20:415–432PubMedCrossRefGoogle Scholar
  24. Yasuta T, Satoh S, Minamisawa K (1999) New assay for rhizobitoxine based on inhibition of 1-aminocyclopropane-1-carboxylate synthase. Appl Environ Microbiol 65:849–852PubMedGoogle Scholar
  25. Yuhashi KI, Ichikawa N, Ezura H, Akao S, Minakawa Y, Nukui N, Yasuta T, Minamisawa K (2000) Rhizobitoxine production by Bradyrhizobium elkanii enhances nodulation and competitiveness on Macroptilium atropurpureum. Appl Environ Microbiol 66:2658–2663PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  • William C. Ratcliff
    • 1
    Email author
  • Kyra Underbakke
    • 1
  • R. Ford Denison
    • 1
  1. 1.Ecology, Evolution and BehaviorUniversity of MinnesotaMinneapolisUSA

Personalised recommendations