Structural investigation of the O-specific polysaccharides of Morganella morganii consisting of two higher sugars

The lipopolysaccharide of the bacterium Morganella morganii (strain KF 1676, RK 4222) yielded two polysaccharides, PS1 and PS2, when subjected to mild acid degradation followed by GPC. The polysaccharides were studied by 1H and 13C NMR spectroscopy, including two-dimensional COSY, TOCSY, NOESY, 1H, 13C HMQC, and HMBC experiments. Each polysaccharide was found to contain a disaccharide repeating unit consisting of two higher sugars, 5-acetamidino-7-acetamido-3,5,7,9-tetradeoxy- l- glycero- d- galacto-non-2-ulosonic acid (a derivative of 8-epilegionaminic acid, 8eLeg5Am7Ac) and 2-acetamido-4- C-(3′-carboxamide-2′,2′-dihydroxypropyl)-2,6-dideoxy- d-galactose (shewanellose, She). The two polysaccharides differ only in the ring size of shewanellose and have the following structures: PS1 →8)-α-8eLeg p5Am7Ac-(2→3)-β-She f-(1→ PS2 →8)-α-8eLeg p5Am7Ac-(2→3)-β-She p-(1→ Shewanellose has been previously identified in a phenol-soluble polysaccharide from Shewanella putrefaciens A6, which shows a close structural similarity to PS2. Graphic