Structure and genetics of the O-antigen of Enterobacter mori GmNs1 containing 5-N-acetyl-7-N-(3-hydroxybutyryl)pseudaminic acid

The O-antigen (O-polysaccharide, OPS) is an essential component of lipopolysaccharide on the surface of Gram-negative bacteria and plays an important role in interaction with different host organisms, including animals and plants. In this study, we investigated the chemical structure and characterized the gene cluster of OPS from bacterium Enterobacter mori GmNs1. As judged by sugar analyses along with NMR spectroscopy data, E. mori GmNs1 O-antigen has a trisaccharide O-unit with the following structure: →4)-β-Psep5Ac7(3Hb)-(2 → 6)-β-D-Galf-(1 → 3)-β-D-Galp-(1→ where Psep5Ac7(3Hb) is 5-N-acetyl-7-N-(3-hydroxybutyryl)-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid. The OPS gene cluster of E. mori GmNs1 located between conserved genes galF and gnd was analyzed. Most genes necessary for the O-antigen biosynthesis were found in the cluster and their functions were tentatively assigned by comparison with sequences in the available databases.