Abstract: Structural studies of the two O-specific polysaccharide(s) and biological activity of the lipopolysaccharide from Azospirillum brasilense SR8 toward plants

STRUCTURAL STUDIES OF THE TWO O-SPECIFIC POLYSACCHARIDE(S) AND BIOLOGICAL ACTIVITY OF THE LIPOPOLYSACCHARIDE FROM AZOSPIRILLUM BRASILENSE SR8 TOWARD PLANTS

E.N. Sigida^a, Yu.P. Fedonenko^a, A.S. Shashkov^b, Ph.V. Toukach^b, A.V. Shelud’ko^a, E.L. Zdorovenko^b, Yu.A. Knirel^b, S.A. Konnova^a,c

^aInstitute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, Saratov, Russia
^bN.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
^cN.G. Chernyshevsky Saratov State University, Saratov, Russia

KEYWORDS: Lipopolysaccharide; Structure; NMR simulation; Azospirillum brasilense; Root hair deformation; Chemotaxis

International Journal of Biological Macromolecules, 2019, v. 126, pp. 246-253

DOI: 10.1016/j.ijbiomac.2018.12.229

Lipopolysaccharide (LPS) was extracted from dry bacterial cells of plant growth promoting bacterium Azospirillum brasilense SR8 (IBPPM 5). The O-specific polysaccharide (OPS) was obtained by mild acid hydrolysis of the lipopolysaccharide and studied by sugar analysis, ¹H and ¹³C NMR spectroscopy, including COSY, TOCSY, ROESY, and ¹H,¹³C HSQC and HMBC experiments, computational NMR-based structure analysis, and Smith degradation. The OPS was shown to contain two types of repeating units of the following structure:

                            b-D-Glcp(1
                                     |4
-2)-a-L-Rhap(1-3)-a-L-Rhap(1-3)-a-L-Rhap(1-    (1)

       b-D-GalpNAc4OMe(1
                       |4
-4)-a-L-Rhap(1-3)-b-D-ManpNAc(1-               (2)

The OPS of A. brasilense SR8 was structurally close to that of A. brasilense 54, for which structure 1 has been reported earlier (Fedonenko et al., 2011) whereas to our knowledge structure 2 has not been found in bacterial saccharides. Treatment of wheat seedling roots with LPS of A. brasilense SR8 increased the number of root hair deformations as compared to seedlings grown without LPS, but had no effect on adsorption of the bacteria to the root surface. A. brasilense SR8 was found to be able to utilize LPS of several structurally related Azospirillum strains.

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