Diversity of monosaccharides and glycosidic linkages on extracellular polysaccharides of the microalga Ankistrodesmus (Chlorophyceae)

ABSTRACT The diversity of monosaccharides and glycosidic linkages of extracellular polysaccharide (EPS) of high molecular weight were studied in strains morphologically assigned to the genus Ankistrodesmus. EPSs of seven strains were similar in both monosaccharides and glycosidic linkages, but showed exclusive characteristics or enough differences in proportions to distinguish strains. Fucose, glucose, rhamnose, mannose and galactose occurred in relatively high percentages in all strains. The strain CCMA-UFSCar 423, excluded from the genus Ankistrodesmus by the molecular marker tufA, was the only one containing galacturonic acid. Arabinose was found only in one A. densus strain (CCMA-UFSCar 239). The species A. densus and A. stipitatus, which are known to have, respectively, stable mucilaginous capsules and pads in aqueous media, presented high percentages of the hydrophobic fucose and rhamnose on their polysaccharides. However, the strain CCMA-UFSCar 83, the only non-colonial A. densus, had low proportions of rhamnose. We also found variations in glycosidic linkages, and some of them were specific to one strain (e.g. 1-3 glucose in A. stipitatus). Conversely, the absence of common linkages was noteworthy for the strain outside the Ankistrodesmus clade, the CCMA-UFSCar 423. The data revealed important diversity in monosaccharides and linkages of the EPS within a single microalgae genus, and an important intraspecific diversity using a single growing condition. These differences could be useful as potential chemotaxonomic tools to help discriminating the Ankistrodesmus genus or species, but also for future studies on intraspecific diversity within the genus. Moreover, the results show the relevance of studying and conserving closely related strains to preserve biodiversity. The diverse composition of high molecular weight EPSs shows a great potential for prospecting EPSs of economic interest.