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Roles of poly-3-hydroxybutyrate (PHB) and glycogen in symbiosis of Sinorhizobium meliloti with Medicago sp.

Marsha Saldanha^2,

Kristopher J. Shelswell^2,

¹ Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
² Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada

Correspondence
Chunxia Wang
cwang{at}vbi.vt.edu

Poly-3-hydroxybutyrate (PHB) and glycogen are major carbon storage compounds in Sinorhizobium meliloti. The roles of PHB and glycogen in rhizobia–legume symbiosis are not fully understood. Glycogen synthase mutations were constructed by in-frame deletion (glgA1) or insertion (glgA2). These mutations were combined with a phbC mutation to make all combinations of double and triple mutants. PHB was not detectable in any of the mutants containing the phbC mutation; glycogen was not detectable in any of the mutants containing the glgA1 mutation. PHB levels were significantly lower in the glgA1 mutant, while glycogen levels were increased in the phbC mutant. Exopolysaccharide (EPS) was not detected in any of the phbC mutants, while the glgA1 and glgA2 mutants produced levels of EPS similar to the wild-type. Symbiotic properties of these strains were investigated on Medicago truncatula and Medicago sativa. The results indicated that the strains unable to synthesize PHB, or glycogen, were still able to form nodules and fix nitrogen. However, phbC mutations caused greater nodule formation delay on M. truncatula than on M. sativa. Time-course studies showed that (1) the ability to synthesize PHB is important for N₂ fixation in M. truncatula nodules and younger M. sativa nodules, and (2) the blocking of glycogen synthesis resulted in lower levels of N₂ fixation on M. truncatula and older nodules on M. sativa. These data have important implications for understanding how PHB and glycogen function in the interactions of S. meliloti with Medicago spp.

Present address: Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd, Ottawa, ON KlH 8M5, Canada.

Present address: Department of Microbiology and Immunology, University of British Columbia, 2329 West Mall, Vancouver, BC V6T 1Z4, Canada.

This article has been cited by other articles:

				C. Wang, X. Sheng, R. C. Equi, M. A. Trainer, T. C. Charles, and B. W. S. Sobral Influence of the Poly-3-Hydroxybutyrate (PHB) Granule-Associated Proteins (PhaP1 and PhaP2) on PHB Accumulation and Symbiotic Nitrogen Fixation in Sinorhizobium meliloti Rm1021 J. Bacteriol., December 15, 2007; 189(24): 9050 - 9056. [Abstract] [Full Text] [PDF]