Full structural characterization of an extracellular polysaccharide produced by the freshwater cyanobacterium oscillatoria planktothrix FP1

Cyanobacteria, also known as blue-green algae or Cyanophyta, represent one of the oldest forms of life on Earth. The organisms exhibit a high degree of biological adaptation and comprise a large group of aquatic and photosynthetic oxygenic prokaryotes that obtain their energy through photosynthesis. Cyanobacterial extracellular polysaccharides are high-molecular-mass hetero-polysaccharides that are present on or released onto the cell surface and are characterized by high variability. In the present work we defined the structure of the extracellular polysaccharide produced by the freshwater cyanobacterium Oscillatoria planktothrix FP1. The structural determination, which was achieved by chemical, spectroscopic, and computational analyses, indicates a novel pentasaccharide repeating unit made up of glucose, mannose, and 2-deoxy-D-ribo-hexose, that has never previously been found in Nature. The elucidation of the structural and conformational features of the extracellular polysaccharide from Oscillatoria planktothrix is a first step toward understanding the biology of these important and interesting microorganisms. Cyanobacteria (blue-green algae) are one of the oldest photosynthetic forms of life on Earth. Here we present the structural characterization of the exopolysaccharide produced by the title organism and show that it is composed of a pentasaccharide repeating unit made up of a new deoxy sugar.