The structural characterization of lipopolysaccharides has critical implications for some biomedical applications, and marine bacteria are an inimitable source of new glyco-structures potentially usable in medicinal chemistry. On the other hand, lipopolysaccharides of marine Gram-negative bacteria present certain structural features that can help the understanding of the adaptation processes. The deep-sea marine Gram-negative bacterium Idiomarina zobellii KMM 231T, isolated from a seawater sample taken at a depth of 4000 m, represents an engaging microorganism to investigate in terms of its cell wall components. Here, we report the structural study of the R-type lipopolysaccharide isolated from I. zobellii KMM 231T that was achieved through a multidisciplinary approach comprising chemical analyses, NMR spectroscopy, and MALDI mass spectrometry. The lipooligosaccharide turned out to be characterized by a novel and unique pentasaccharide skeleton containing a very short mono-phosphorylated core region and comprising terminal neuraminic acid. The lipid A was revealed to be composed of a classical disaccharide backbone decorated by two phosphate groups and acylated by i13:0(3-OH) in amide linkage, i11:0 (3-OH) as primary ester-linked fatty acids, and i11:0 as a secondary acyl chain.
Keywords: Idiomarina zobellii; MALDI mass spectrometry; NMR spectroscopy; deep-sea; lipid A; lipooligosaccharide; marine bacteria.