Structural elucidation of an extracellular polysaccharide produced by the marine fungus Aspergillus versicolor

A homogenous extracellular polysaccharide, designated AWP, was isolated from the fermented liquid of the marine fungus Aspergillus versicolor from the coral Cladiella sp. and purified by anion-exchange and size-exclusion chromatography (SEC). Chemical and spectroscopic analyses, including one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy showed that AWP consisted of glucose and mannose in a molar ratio of 8.6:1.0, and its average molecular weight was estimated to be 500 kDa. AWP is a slightly branched extracellular polysaccharide. The backbone of AWP is mainly composed of (1→6)-linked α-d-glucopyranose residues, slightly branched by single α-d-mannopyranose units attached to the main chain at C-3 positions of the glucan backbone. The investigation demonstrated that AWP is a novel extracellular polysaccharide different from those of other marine microorganisms.

► AWP was obtained from the fermented liquid of Aspergillus versicolor.
► Structure of AWP was elucidated by GC–MS, FTIR and NMR.
► The backbone of AWP consisted of glucopyranose units.
► The side chain contained mannopyranose units.
► AWP was a novel polysaccharide different from other exopolysaccharides.