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

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, H-1 and C-13 NMR spectroscopy, including H-1 H-1 COSY, TOCSY, ROESY, and H-1, C-13 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: beta-D-Glcp-(1 -> 4) -> 2)-alpha-L-Rhap-(1 -> 3)-alpha-L-Rhap-(1 -> 3)-alpha-L-Rhap-(1 -> 1 beta-D-Ga1pNAc4Me-(1 ->-4) -> 4)-alpha-L-Rhap-(1 -> 3)-beta-D-ManpNAc-(1 -> 2 Both OPS structures are present in A. brasilense 54, from which structure 1 has been reported earlier (Fedonenko et al., 2011), whereas to our knowledge structure 2 has not been hitherto 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 able to utilize LPS of several structurally related Azospirillum strains. (C) 2019 Elsevier B.V. All rights reserved.