ABSTRACT
Lipopolysaccharides (LPSs) are major components of the outer membrane of Gram-negative bacteria and are essential for their growth and survival. They act as a structural barrier and play an important role in the interaction with eukaryotic hosts. Here we demonstrate that a photosynthetic Bradyrhizobium strain, symbiont of Aeschynomene legumes, synthesizes a unique LPS bearing a hopanoid covalently attached to lipid A. Biophysical analyses of reconstituted liposomes indicate that this hopanoid-lipid A structure reinforces the stability and rigidity of the outer membrane. In addition, the bacterium produces other hopanoid molecules not linked to LPS. A hopanoid-deficient strain, lacking a squalene hopene cyclase, displays increased sensitivity to stressful conditions and reduced ability to survive intracellularly in the host plant. This unusual combination of hopanoid and LPS molecules may represent an adaptation to optimize bacterial survival in both free-living and symbiotic states.
Subject(s)
Bradyrhizobium/physiology , Fabaceae/microbiology , Lipid A/metabolism , Plant Root Nodulation , Root Nodules, Plant/microbiology , Triterpenes/metabolism , Fabaceae/ultrastructure , Lipid A/chemistry , Molecular Structure , Root Nodules, Plant/ultrastructure , SymbiosisABSTRACT
The lipopolysaccharide of Pseudomonas aeruginosa O-12 was studied by strong alkaline and mild acid degradations and dephosphorylation followed by fractionation of the products by GPC and high-performance anion-exchange chromatography and analyses by ESI FT-MS and NMR spectroscopy. The structures of the lipopolysaccharide core and the O-polysaccharide repeating unit were elucidated and the site and the configuration of the linkage between the O-polysaccharide and the core established. The core was found to be randomly O-acetylated, most O-acetyl groups being located on the terminal rhamnose residue of the outer core region.
Subject(s)
Endotoxins/chemistry , Fucose/analogs & derivatives , Lipopolysaccharides/chemistry , O Antigens/chemistry , Pseudomonas aeruginosa/chemistry , Carbohydrate Sequence , Chromatography, Gel , Chromatography, High Pressure Liquid , Chromatography, Ion Exchange , Deoxy Sugars/analysis , Fucose/analysis , Heptoses/analysis , Isomerism , Lipopolysaccharides/isolation & purification , Magnetic Resonance Spectroscopy , Molecular Sequence Data , Molecular Weight , Monosaccharides/analysis , Oligosaccharides, Branched-Chain/chemistry , Polysaccharides, Bacterial/chemistry , Spectrometry, Mass, Electrospray Ionization , Sugar Acids/analysisABSTRACT
A phosphorylated core-lipid A backbone oligosaccharide that carries a disaccharide remainder of the first O-antigen repeating unit was derived by strong alkaline degradation following mild hydrazinolysis of the lipopolysaccharide of Pseudomonas aeruginosa immunotype 4 (serogroup O-1). The structure of the oligosaccharide was determined using ESI MS and NMR spectroscopy and it was demonstrated that 2-acetamido-2,6-dideoxy-D-glucose is the first monosaccharide of the O-polysaccharide that is linked to the LPS core. These data define the structure of the biological repeating unit of the O-antigen.