Structural and conformational study of the O-polysaccharide produced by the metabolically versatile photosynthetic bacterium Rhodopseudomonas palustris strain BisA53

•Rhodopseudomonas palustris is a photosynthetic metabolically versatile bacterium.•The LPS O-polysaccharide from R. palustris has been extracted and purified.•This strain produced a polymer with a trisaccharide repeating unit and a new sugar.•NMR spectroscopy and molecular mechanic and dynamic simulation studies lead to the structural and conformational features. Rhodopseudomonas palustris is a purple photosynthetic bacterium characterized by a versatile nature and a remarkable ability to adapt to various environments. In this work, we focused our attention to its membrane characteristics and defined the structural and conformational features of the O-chain polysaccharide of LPS isolated from R. palustris strain BisA53. This strain produces a polymer with a trisaccharide repeating unit characterized by d-rhamnose, 3-deoxy-d-lyxo-2-heptulosaric acid (Dha), and a novel C-branched monosaccharide, a 4-amino-4,6-dideoxy-3-C-methyl-2-O-methyl-α-l-glucopyranose whose absolute configuration has been determined by a combination of 2D NMR spectroscopy and molecular mechanic and dynamic simulation.