Structural characterization of the core region from the lipopolysaccharide of the haloalkaliphilic bacterium Halomonas alkaliantarctica strain CRSS

Halophilic and halotolerant Gram-negative bacteria are microorganisms which thrive in high salt
environments. LPS are the major components of their outer leaflet, nevertheless very little is known
about the role of this molecules in the adaptation mechanisms of extremophiles. Recently we
determined the O-chain repeating unit structure of the LPS from Halomonas alkaliantarctica strain
CRSS, an haloalkaliphilic Gram-negative bacterium isolated from salt sediments of a saline lake in
Cape Russell in Antarctic continent. The polysaccharide is constituted of the trisaccharidic repeating
unit:->3)-beta-L-Rhap-(1->4)-alpha-L-Rhap-(1->3)-alpha-L-Rhap-(1->. In this paper we report the complete
core LPS structure from this bacterium. The LPS was hydrolyzed both under mild acid and strong
alkaline conditions. The MALDI spectra showed the presence of two glycoforms. The most abundant
was recovered after HPAEC purification of the alkaline hydrolyzed product and was characterized by
means of 2D-NMR spectroscopy. A comparison of the MALDI-PSD spectra ofthe two glycoforms
suggested that the branched heptose was not stoichiometrically substituted.