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

ABSTRACT

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