Presence of N-l-lactyl-d-perosamine residue in the sheath-forming polysaccharide of Thiothrix fructosivorans

Thiothrix fructosivorans forms a microtube (sheath) that encloses a line of cells. This sheath is an assemblage of [→4)-GlcN-(1 → 4)-Glc-(1→]n with side chains of Rha4N-(1 → 3)-Fuc(1→ at position 3 of Glc. The sheath-forming polysaccharide (SFP) may have some substitutions but this is not yet confirmed. To investigate the possible substitutions, the sheath was prepared by mild treatments. Solid-state NMR analysis suggested the presence of N-substitution. The sheath was hydrolyzed with concentrated HCl at 0 °C, followed by derivatization with 4-aminobenzoic acid ethyl ester (ABEE). The presence of N-lactyl-Rha4N-Fuc-ABEE was suggested by NMR spectroscopy. Lactic acid was determined to be the l-isomer by chiral HPLC analysis. To estimate the N-lactylation degree, the sheath was N-acetylated. N-Acetyl-Rha4N-Fuc-ABEE and N-lactyl-Rha4N-Fuc-ABEE were then collectively recovered, and their abundance ratio was determined to be 1:4 by NMR analysis. When hydrolysis was performed at 40 °C, GlcNAc-ABEE was obtained. For estimation of the N-acetylation degree, the sheath was N-acetylated with deuterated acetic anhydride and then N-acetyl-GlcN-ABEE was prepared. The content of deuterated N-acetyl-GlcN-ABEE was determined to be 50% based on the relative intensity of the acetyl proton signal in the 1D-1H NMR spectrum. It was concluded that Rha4N is mostly N-l-lactylated and GlcN is substoichiometrically N-acetylated.