Structural characterisation of a fucose-rich acidic extracellular polysaccharide produced by Lindavia intermedia in New Zealand lakes

Lake snow is a nuisance mucilaginous material composed of extracellular polymeric substances (EPS), produced by the invasive centric diatom Lindavia intermedia in New Zealand lakes. This study presents the extraction, isolation, and structural characterisation of both non-attached and attached EPS from lake snow aggregates collected from Lake Wānaka, New Zealand. Monosaccharide composition and glycosyl linkage analyses revealed that the EPS are highly heterogeneous, with the attached EPS enriched in galactose, mannose, and glucuronic acid, and containing high molecular weight polysaccharides. Endogenous O -methylation was observed on several sugars, including fucose and rhamnose. A high molecular weight, fucose-rich acidic polysaccharide was purified from the attached EPS using ion-exchange and size-exclusion chromatography. Structural elucidation by glycosyl linkage analysis and NMR spectroscopy identified a backbone composed of alternating →2,3)-α-D-Gal f -(1 → and →3,4)-β-D-Glc p A-(1 → residues with branching by terminal α-Fuc p residues that are endogenously 2,3- or 2,3,4- O -methylated. These structural features are probably responsible for the adhesive and biofouling properties of lake snow. This study reports the first detailed structural characterisation of a purified, non-chitinous polysaccharide from the EPS of a freshwater centric diatom, providing new insights into the persistence and ecological impact of L. intermedia in freshwater environments. • Extracellular polymeric substances were isolated from New Zealand lake snow. • Monosaccharide and linkage analyses showed highly heterogeneous structures. • A novel high molecular weight, fucose-rich acidic polysaccharide was purified. • The structure was determined by glycosyl linkage and NMR spectroscopic analysis. • This polysaccharide may be responsible for the formation of lake snow aggregates.