Teichuronic Acid-Like Polymer in the Cell Wall of Rathayibacter sp. VKM Ac-2856 – A New Type of Acidic Glycopolymer for Representatives of the Genus

Using chemical methods and methods of NMR spectroscopy, the structures of three cell wall glycopolymers of Rathayibacter sp. VKM Ac-2856 (family Microbacteriaceae, class Actinomycetes), isolated from Brachypodium distachyon (family Poaceae), were determined. The first polymer, an unsubstituted mannan with a repeating unit, →2)-α-d-Manp-(1→, was discovered in the cell walls of Rathayibacter for the first time. The second, a rhamnomannan, consists of regularly alternating residues of α-d-rhamnose and α-d-mannose and has non-stoichiometric substitution with β-d-Xylp residues in a 3 : 1 ratio, →2)-α-d-Rhap-(1→3)-[β-d-Xylp-(1→2)]-α-d-Manp-(1→. The third, a minor, teichuronic acid-like polymer with a trisaccharide repeating unit and R-pyruvic acid, bears side residues of β-d-glucuronic acid, →3)-α-d-[4,6-R-Pyr]-Galp-(1→3)-β-d-Glcp-(1→6)-[β-d-GlcpA-(1→3)]-α-d-Manp-(1→. The latter distinguishes this polymer from teichuronic acids, which contain uronic acid residues in the main chain. Structure of the teichuronic acid-like polymer is novel for both Rathayibacter and prokaryotes in general. The results of this study demonstrate structural diversity of microbial glycopolymers and are consistent with the previously reported data on the species-specific composition of glycopolymers in the representatives of the genus Rathayibacter.