A physico-chemical comparative study on extracellular carbohydrate polymers from five desert algae

Hydrodynamic properties of five newly isolated algal extracellular polysaccharides with putative adhesive properties are described, using a combination of size exclusion chromatography, total or ‘multi-angle’ laser light scattering and analytical ultracentrifugation. The respective polysaccharides had been extracted from four filamentous cyanobacteria: Microcoleus vaginatus, Scytonema javanicum, Phormidium tenue and Nostoc sp. and a coccoid single-cell green algae Desmococcus olivaceus that had been separated from desert algal crusts of the Chinese Tegger Desert. SEC/MALLS experiments showed that the saccharides had diverse weight average molecular weights ranging from 4000 to 250,000 g/mol and all five showed either bi-modal or tri-modal molecular weight distribution profiles. Use of the Mark–Houwink–Kuhn–Sakurada (MHKS) scaling relationship between sedimentation coefficient and (weight average) molecular weight for the five samples, assuming a homologous conformation series revealed an MHKS b exponent of (0.33±0.04), suggesting a conformation between that of a stiff rod (b∼0.18) and a random coil (b∼0.4–0.5), i.e. a ‘ flexible rod’ or ‘stiff coil’.