Chemical structures of the secondary cell wall polymers (SCWPs) isolated from bovine mastitis Streptococcus uberis

The cell envelope of Gram-positive bacteria is decorated with a variety of polysaccharides. In this study wall teichoic acid (WTA) and neutral polysaccharides were isolated from the cell envelope of bovine mastitis Streptococcus uberis. The polysaccharides were released by lysozyme treatment, and purified by hydrophobic interaction chromatography. Further separation was achieved utilizing anion-exchange chromatography which yielded two products, that is, a neutral polysaccharide with a high content of Rha and less Glc (rhamnan) and an anionic phosphate-rich one containing glycerol and Glc (WTA). The structures of these molecules were elucidated applying 1D and 2D nuclear magnetic resonance experiments as well as chemical analyses. In the rhamnan sample two independent molecules were identified, that is, a glucorhamnan with the structure →2)-α-l-Rhap-(1→3)-[α-d-Glcp-(1→2)-]α-l-Rhap-(1→, and a homopolymeric rhamnan →2)-α-l-Rhap-(1→3)-α-l-Rhap-(1→. The WTA comprised a polyphosphoglycerol chain substituted nonstoichiometrically with β-Glcp.