Structure of perosamine-containing polysaccharide, a component of the sheath of Thiothrix fructosivorans

A sheath-forming and sulfur-oxidizing bacterium, Thiothrix fructosivorans, was heterotrophically cultured. The sheath, which is an extracellular microtube, was prepared by selectively removing the cells using lysozyme, sodium dodecyl sulfate, and sodium hydroxide. Solid-state 13C-nuclear magnetic resonance (NMR) spectrum revealed that the sheath is assembled from a glycan possessing acetyl and methyl groups. When the sheath was deacetylated, the original microtube structure was lost and the sheath became soluble under acidic conditions, revealing the importance of acetyl groups in maintaining the sheath structure. Equimolar d-glucose, d-glucosamine, and l-fucose were detected in the acid hydrolysate of the sheath by gas liquid chromatography. In addition to these sugars, β-GlcN-(1 → 4)-Glc and unidentified sugar were detected by analyzing the hydrolysate using high-performance liquid chromatography analysis. 1H and 13C NMR spectroscopy was used to identify a disaccharide composed of 4-deoxy-4-aminorhamnose (perosamine, Rha4N) and fucose. N-Acetyl-perosamine prepared from the disaccharide was polarimetric and exhibited a d-configuration. The previously unidentified disaccharide was found to be α-d-Rhap4N-(1 → 3)-d-Fuc. According to 1H and 13C NMR analyses, the deacetylated sheath-forming polysaccharide was found to h have a main chain of [→ 4)-β-d-GlcpN-(1 → 4)-β-d-Glcp-(1 →]n, to which disaccharide side chains of α-d-Rhap4N-(1 → 3)-α-l-Fucp-(1 → were attached at position 3 of Glc.