Characterization and symbiotic importance of acidic extracellular polysaccharides of Rhizobium sp. strain GRH2 isolated from acacia nodules.
Rhizobium sp. wild-type strain GRH2 was originally isolated from root nodules of the leguminous tree Acacia cyanophylla and has a broad host range which includes herbaceous legumes, e.g., Trifolium spp. We examined the extracellular exopolysaccharides (EPSs) produced by strain GRH2 and found three independent glycosidic structures: a high-molecular-weight acidic heteropolysaccharide which is very similar to the acidic EPS produced by Rhizobium leguminosarum biovar trifolii ANU843, a low-molecular-weight native heterooligosaccharide resembling a dimer of the repeat unit of the high-molecular-weight EPS, and low-molecular-weight neutral beta (1,2)-glucans. A Tn5 insertion mutant derivative of GRH2 (exo-57) that fails to form acidic heteropolysaccharides was obtained. This Exo- mutant formed nitrogen-fixing nodules on Acacia plants but infected a smaller proportion of cells in the central zone of the nodules than did wild-type GRH2. In addition, the exo-57 mutant failed to nodulate several herbaceous legume hosts that are nodulated by wild-type strain GRH2.
Department of Microbiology, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Cientificas, Granada, Spain.
I M
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Lopez-Lara
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Orgambide
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Dazzo
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J
Olivares
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Toro
D000045:Acacia / Q000033:anatomy & histology / Q000382:microbiology*; D007887:Fabaceae / Q000033:anatomy & histology / Q000382:microbiology*; D014644:Genetic Variation; D006027:Glycosides / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D009005:Monosaccharides / Q000032:analysis; D016296:Mutagenesis; D009844:Oligosaccharides / Q000737:chemistry; D010946:Plants, Medicinal; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000378:metabolism; D012231:Rhizobium / Q000737:chemistry* / Q000502:physiology*; D013045:Species Specificity; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013559:Symbiosis / Q000502:physiology*
D006027:Glycosides; D009005:Monosaccharides; D009844:Oligosaccharides; D011135:Polysaccharides, Bacterial