The core and O-polysaccharide structure of the Caulobacter crescentus lipopolysaccharide

[Display omitted] •The study reports the complete structure of the smooth lipopolysaccharide from the common model organism, Caulobacter crescentus.•Caulobacter crescentus’ O-antigen is the anchor molecule for supporting the bacterium’s S-layer.•The O-antigen structure is a repeating heptamer containing the rare monosaccharide N-acetylperosamine.•A previously unknown rhamnan polysaccharide was discovered and its structure was determined. Here we describe the analysis of the structure of the lipopolysaccharide (LPS) from Caulobacter crescentus strain JS1025, a derivative of C. crescentus CB15 NA1000 with an engineered amber mutation in rsaA, leading to the loss of the protein S-layer and gene CCNA_00471 encoding a putative GDP-l-fucose synthase. LPS was isolated using an aqueous membrane disruption method. Polysaccharide and core oligosaccharide were produced by mild acid hydrolysis and analyzed by nuclear magnetic resonance spectroscopy and chemical methods. Spectra revealed the presence of two polysaccharides, one of them, a rhamnan, could be removed using periodate oxidation. Another polymer, built from 4-amino-4-deoxy-d-rhamnose (perosamine), mannose, and 3-O-methyl-glucose, should be the O-chain of the LPS according to genetic data. The attribution of the rhamnan as a part of LPS or a separate polymer was not possible.