Lipooligosaccharide architecture in Acinetobacter modestus CM11G: a non-pathogenic strain

The Acinetobacter genus comprises a multitude of species that have been isolated from both environmental and clinical samples. In recent years, the scientific community has expended considerable effort in characterising the structures of the capsular polysaccharides and lipooligoaccharides (LOS) of A. baumannii, given the increasing mortality rate caused by this species. Comparatively little research has been undertaken for the non-pathogenic species. In the present study, we describe the first case of isolation and identification of the LOS molecule of Acinetobacter modestus CM11G, a Gram-negative bacterium colonising the intestinal crypts of a healthy mouse. By combining spectroscopic and spectrometric analyses with chemical derivatisations, we were able to determine the structure of the entire LOS. The lipid A moiety is composed mainly of hepta-acylated species, a characteristic also observed in other Acinetobacter species. It is extended with a disaccharide of Kdo, which acts as a bridge between the lipid A and the oligosaccharide portion. Indeed, the internal Kdo residue is linked at position O-5 with a novel tetrasaccharide composed of βGlcN(1→2)-βGal(1→6)-αGlc(1→, where the glucose is further substituted at position O-4 with a terminal β-Glc. In contrast, the external Kdo residue does not undergo further substitution, contrary to what generally occurs in the LOS of A. baumannii.