Two distinct sulfated O-polysaccharides from the marine bacterium Vibrio sp. KMM 9700: Genomic prediction and...

Bacteria of the genus Vibrio dwelling in marine environment produce structurally diverse lipopolysaccharides (LPS) that play critical roles in environmental adaptation and host interactions. Here we report the complete structural elucidation of two O-polysaccharides (OPS) from the LPS of Vibrio sp. KMM 9700, isolated from the red alga Polysiphonia sp. Genomic analysis revealed an O-antigen gene cluster containing sulfotransferases (STs), glycosyltransferases (GTs), a PAPS biosynthesis operon, and the dTDP-Rha pathway. A GT and ST pair similar to that in the capsular polysaccharide cluster of V. chaetopteri KMM 8419^T suggested the synthesis of a polysaccharide with α-l-rhamnopyranose (α-L-Rhap) 3-O-sulfate. An additional GT and ST pair in the cluster indicated the biosynthesis of another sulfated polysaccharide. Using chemical analyses, selective modifications, and NMR spectroscopy, we showed that both OPS coexist in the LPS preparation. The major OPS is a tetrasaccharide repeating unit with alternating 6-substituted α-D-Glcp and 2-substituted α-L-Rhap residues, featuring sulfate at O-3 and O-acetyl at O-4 of one α-L-Rhap residue. The minor OPS is a pentasaccharide repeating unit composed exclusively of α-L-Rhap residues with three 3-linked and two 2-linked residues, bearing sulfate groups at O-2 of two specific α-L-Rhap residues. Neither structure has been previously reported in bacterial glycans. The presence of two distinct sulfated OPS in a single Vibrio strain expands the known chemotypic diversity within the genus and suggests a sophisticated surface adaptation mechanism in marine environments.