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The role of PHB metabolism in the symbiosis of rhizobia with legumes


The carbon storage polymer poly-β-hydroxybutyrate (PHB) is a potential biodegradable alternative to plastics, which plays a key role in the cellular metabolism of many bacterial species. Most species of rhizobia synthesize PHB but not all species accumulate it during symbiosis with legumes; the reason for this remains unclear, although it was recently shown that a metabolic mutant of a nonaccumulating species retains the capacity to store PHB in symbiosis. Although the precise roles of PHB metabolism in these bacteria during infection, nodulation, and nitrogen fixation are not determined, the elucidation of these roles will influence our understanding of the metabolic nature of the symbiotic relationship. This review explores the progress that was made in determining the biochemistry and genetics of PHB metabolism. This includes the elucidation of the PHB cycle, variations in PHB metabolism among rhizobial species, and the implications of these variations, while proposing a model for the role of PHB metabolism and storage in symbiosis.

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The authors would like to thank Scott Clark for critical appraisal and helpful discussion. Research on PHB metabolism in the laboratory of T. C. Charles is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Agribiotics, Inc.

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Correspondence to Trevor C. Charles.

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Trainer, M.A., Charles, T.C. The role of PHB metabolism in the symbiosis of rhizobia with legumes. Appl Microbiol Biotechnol 71, 377–386 (2006).

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  • Rhizobium
  • PHAs
  • Malic Enzyme
  • Indeterminate Nodule
  • Determinate Nodule