Free-living nitrogen-fixing bacteria of the genus Azospirillum colonize the rhizosphere of various plants, e.g. agriculturally important crops, and have a positive effect on their growth and yield [1]. Located on the cell surface, lipopolysaccharides (LPS) of these bacteria play an important role in the establishment and functioning of effective symbiotic associations [2].
The LPS was obtained by the phenol-water procedure from dry bacterial cells of Azospirillum brasilense type strain Sp7. Mild acid hydrolysis of the LPS followed by gel-permeation chromatography on Sephadex G-50 resulted in O-specific polysaccharides, which were studied by composition and methylation analyses, Smith degradation, and 1H and 13C NMR spectroscopy. Structures 1 and 2 were established for two polysaccharides [italics indicates a non-stoichiometric (~65 %) 2-O-methylation of l-rhamnose]:
Additionally, a minor polysaccharide(s) was detected, whose structure(s) was not determined.
Recently, the polysaccharide having the structure 1 (except for O-methylation of rhamnose) was identified as a glycan chain of the glycosylated flagellin of these bacteria [3], whereas the structure 2 was elucidated for the O-specific polysaccharide of A. brasilense Jm6B2 [4]. The presence of methylated and 6-deoxyhexose-enriched polysaccharides, also found in the LPSs of other Azospirillum strains, could increase the hydrophobicity of the cell surface of the bacteria, thus enabling their better adsorption to the roots of the host plant.
This work was supported by the Russian Foundation for Basic Research (Project 11-04-00533).
[1] Fibach-Paldi S. et al., FEMS Microbiol. Lett. 2012, 326:99-108
[2] Steenhoudt O. and Vanderleyden J., FEMS Microbiol. Rev. 2000, 24:487-506
[3] Belyakov A.Y. et al., Carbohydr. Res. 2012, 361:127-132.
[4] Boyko A.S. et al., Carbohydr. Res. 2012, 355:92-95.
