CHEMICAL-STRUCTURE OF THE LIPID-A COMPONENT OF LIPOPOLYSACCHARIDES OFTHE GENUS PECTINATUS

The chemical structure of the lipid A components of smooth-type lipopo lysaccharides isolated from the type strains of strictly anaerobic bee r-spoilage bacteria Pectinatus cerevisiiphilus and Pectinatus frisinge nsis were analyzed. The hydrophilic backbone of lipid A was shown, by controlled degradation of lipopolysaccharide combined with chemical as says and P-31-NMR spectroscopy, to consist of the common beta 1-6-link ed disaccharide of pyranosidic 2-deoxy-glucosamine (GlcN), phosphoryla ted at the glycosidic position and at position 4'. In de-O-acylated li popolysaccharide, the latter phosphate was shown to be quantitatively substituted with 4-amino-4-deoxyarabinose, whereas the glycosidically linked phosphate was present as a monoester. Laser-desorption mass spe ctrometry of free dephosphorylated lipid A revealed that the distal (n on-reducing) GlcN was substituted at positions 2' and 3' with (R)-3-(u ndecanoyloxy)tridecanoic acid, whereas the reducing GlcN carried two u nsubstituted (R)-3-hydroxytetradecanoic acids at positions 2 and 3. Th e lipid A of both Pectinatus species were thus of the asymmetric hexaa cyl type. The linkage of lipid A to polysaccharide in the lipopolysacc haride was relatively resistant to acid-catalyzed hydrolysis, enabling the preparation of a dephosphorylated and deacylated saccharide backb one. Methylation analysis of the backbone revealed that position 6' of the distal GlcN of lipid A was the attachment site of the polysacchar ide. Despite the quantitative substitution of the lipid A 4'-phosphate by 4-amino-4-deoxyarabinose, which theoretically should render the ba cteria resistant to polymyxin, P. cerevisiiphilus was shown to be susc eptible to this antibiotic. P. cerevisiiphilus was, however, also susc eptible to vancomycin and bacitracin, indicating that the outer membra ne of this bacterium does not act as an effective permeability barrier