Structure of the O-antigen of Acinetobacter lwoffii EK30A; identification of D-homoserine, a novel non-sugar component of bacterial polysaccharides

We established a peculiar structure of the O-specific polysaccharide (O-antigen) of a psychrotrophic strain of Acinetobacter lwoffii, EK30A, isolated from a 1.6–1.8 million-year-old Siberian permafrost subsoil sediment sample. The polysaccharide was released by mild acid degradation of the lipopolysaccharide and studied using chemical analyses, Smith degradation, ¹H and ¹³C NMR spectroscopy and mass spectrometry. It was found to contain D-homoserine, which is N-linked to 4-amino-4,6-dideoxy-D-glucose (Qui4N) and is N-acylated itself with acetyl in about half of the repeating units or (S)-3-hydroxybutanoyl group in the other half. The following is the structure of the tetrasaccharide repeating unit of the polysaccharide: →3)-β-D-Quip4NAcyl-(1→6)-α-D-Galp-(1→4)-α-D-GalpNAc-(1→3)-α-D-FucpNAc-(1→ where Acyl stands for either N-acetyl- or N-[(S)-3-hydroxybutanoyl]-D-homoseryl.