O-chain structure from the lipopolysaccharide of the human pathogen Halomonas stevensii strain S18214.

Halomonas stevensii is a Gram-negative, pathogenic, moderately halophilic bacterium isolated from the blood of a renal care patient. It optimally grows at 30-35°C at pH 8-9 and at a sea salt concentration ranging from 3.0% to 7.5%. Gram-negative bacterial infections are closely associated with the presence of the lipopolysaccharides (LPSs) on the outer membrane. These molecules consist of three regions covalently linked: the glycolipid (lipid A), the oligosaccharide region (core region), and the O-specific polysaccharide (O-chain, O-antigen). O-antigen seems to play an important role in the colonization step (adherence) and the ability to bypass host defense mechanisms. For this reason the structure elucidation of the O-chain repeating unit is important to improve knowledge about the role of LPS in the host-pathogen interaction. In this paper, we report the complete structure of the O-chain from the LPS of H. stevensii. The bacterial cells were cultivated and LPS was extracted by the PCP (phenol-chloroform-petroleum ether) method. After mild acid hydrolysis, the lipid A was removed by centrifugation and the obtained polysaccharide was analyzed by means of chemical analysis and one- and two-dimensional NMR spectroscopy giving the following structure: