Structural analysis of the carbohydrate components of the outer membrane of the lipopolysaccharide-lacking cellulolytic ruminal bacterium Fibrobactersuccinogenes S85

The polysaccharides from the outer membrane of the Gram-negative ruminal ba cterium Fibrobacter succinogenes were isolated by phenol/water extraction a nd separated by size-exclusion chromatography in the presence of deoxychola te detergent into a lower-molecular-mass fraction designated 'glycolipid' a nd a high-molecular-mass 'capsular polysaccharide' fraction. Both fractions lacked typical lipopolysaccharide components including 2-keto-3-deoxyoctul osonic acid and 3-hydroxy fatty acids. Carbohydrate components of these fra ctions were represented by two polysaccharides and one oligosaccharide (pos sibly glycolipid) with the following structures: [GRAPHICS] where HEAEP is N-(2-hydroxyethyl)-2-aminoethylphosphonic acid, found for th e first time in natural compounds. The polysaccharides contained pentadecan oic acid and anteisopentadecanoic acid, possibly present as the acyl compon ents. All constituent monosaccharides except L-rhamnose had a D- configurat ion. In addition to having a structural role in the outer membrane, these polysa ccharides may provide protection for this lipopolysaccharide-less bacterium in the highly competitive ruminal environment, as phosphonic acids covalen tly linked to membrane polymers have in the past been attributed the functi on of stabilizing membranes in the presence of phosphatases and lipases.