Poly-3-hydroxybutyrate (PHB) supports survival and reproduction in starving rhizobia

William C. Ratcliff, Supriya V. Kadam, Robert Ford Denison

Research output: Contribution to journalArticlepeer-review

112 Scopus citations


The carbon that rhizobia in root nodules receive from their host powers both N2 fixation, which mainly benefits the host, and rhizobium reproduction. Rhizobia also store energy in the lipid poly-3-hydroxybutyrate (PHB), which may enhance rhizobium survival when they are carbon limited, either in nodules or in the soil between hosts. There can be a conflict of interest between rhizobia and legumes over the rate of PHB accumulation, due to a metabolic tradeoff between N2 fixation and PHB accumulation. To quantify the benefits of PHB to carbon-limited rhizobia, populations of genetically uniform rhizobia with high vs. low PHB (confirmed by flow cytometry) were generated by fractionating Sinorhizobium meliloti via density gradient centrifugation, and also by harvesting cells at early vs. late stationary phase. These rhizobia were starved for 165 days. PHB use during starvation was highly predictive of both initial reproduction and long-term population maintenance. Cultured S. meliloti accumulated enough PHB to triple their initial population size when starved, and to persist for c. 150 days before the population fell below its initial value. During the first 21 days of nodule growth, undifferentiated S. meliloti within alfalfa nodules accumulated enough PHB to support significant increases in reproduction and survival during starvation.

Original languageEnglish (US)
Pages (from-to)391-399
Number of pages9
JournalFEMS microbiology ecology
Issue number3
StatePublished - Sep 2008


  • Cheating
  • Coevolution
  • Fitness
  • Mutualism
  • Symbiosis
  • Tradeoff


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