Unusual Lipid A from a cold adapted bacterium: detailed structural characterization

Colwellia psychrerythraea 34H is a Gram-negative cold-adapted microorganism that adopts many strategies to cope with the limitations due to the low temperatures of its habitat. In this study, we reported the complete characterization of the lipid A moiety from the lipopolysaccharide of Colwellia, to find out if structural features could be linked to the cold-adaptation strategy. The lipid A and its partially deacylated derivative were completely characterized by means of high resolution mass spectrometry, NMR spectroscopy, and chemical analysis. An unusual structure, consisting of 3-hydroxy unsaturated tetradecenoic acid as component of the primary acylation pattern, was identified. In addition, the presence of a partially acylated phosphoglycerol moiety on the secondary acylation site at 3-position of the reducing GlcN caused a tremendous natural heterogeneity of the lipid A structure. Biological activity assays indicated that Colwellia psychrerythraea 34H lipid A did not show any either agonistic or antagonistic effect when tested in human macrophages.