Polysaccharides in desert reclamation: Compositions of exocellular proteoglycan complexes produced by filamentous blue-green and unicellular green edaphic algae

Abstract

The filamentous blue-green alga Nostoc calcicola Geitler, strain 79WA01, showed a peak production of ∼70% of its biomass as a mixture of exocellular proteoglycan complexes, containing 3–30% of a polypeptide moiety and >70% of a complex glycuronoglycan. The former contained high proportions of Asp, Glu, Arg, and amido-NH 3, in addition to ∼35% of “hydrophobic” amino-acids. The latter varied in composition in different fractions: GalA (2.5–10.3%), GlcA (4.7–11.5%), Glc (11.7–39.0%), Xyl (5.7–17.9%), Man (2.7–9.5%), Gal (5.7–9.5%), Fuc (1.5–11.1%), Ara (1.9–4.3%), and Rha (1.4–4.4%). None of the fractions showed a stoichiometric ratio of sugar residues. Palmelloid cells of three unicellular green soil-algae of the genus Chlamydomonas yielded ∼70% of their dry weight as capsular mucilage. About 50% of the sodium salt of this material was soluble in water, and contained 3–12% of polypeptide and 88–97% of glycuronoglycan (GlcA:Glc:Xyl = 1:1:3 for C. humicola Lucksch, and GlcA:Gal = 1:2 for C. peterfii Gerloff and C. sajao Lewin). These categorical differences in sugar composition, together with narrow composition distributions, suggested regular structures for the glycuronoglycans. The remainder of the mucilages contained essentially the same glycuronoglycan chains, but a higher proportion of polypeptide. These materials did not form true solutions in water, but dispersed as microgel particles.