Cyanobacterial polysaccharides, sacran, which are extracted from jelly Aphanothece sacrum biomaterials, have an ultra-high molecular weight (29 MDa), and their sugar constituents have 11 mol % carboxylic acid and 12 mol % sulfate content to monosaccharide residues.  Then sacran behaved as a supergiant anion assembly. For example, the concentrations of Ca ions and Fe ions in the river where Aphanothece sacrum are found were 21 ppm and 86 ppb, respectively, and the concentrations of Ca ions and Fe ions in Aphanothece sacrum biomaterials were 270-400 ppm and 17-25 ppm, respectively. From this result, it was clear that the enrichment of the metal ions from the river water had occurred (12- to 19-fold for Ca ions and 200- to 290-fold for Fe ions). This suggests that the extracellular polysaccharide sacran functioned within a living organism for metal ions condensation.  Consequently, the role of the sacran in the formation of the jelly material (gels) was examined by qualitatively evaluating the gel formation capability. The examination indicated that sacran adsorbed efficiently trivalent rare earth metal ions such as lanthanide ions. Comparing between sacran and alginate whose molecular weight is lower than sacran and has only carboxylate, sacran can adsorb lanthanide ions at very low solution concentration to form gels. Cryo-TEM of quick-frozen samples of the dispersion for small gels were observed. The polysaccharides (sacran and alginate) did not form specific organization structures in calcium (II) dichloride or tin (IV) tetrachloride solution, while fibrous nano-structures were generated in the neodymium (III) trichloride solution. This may be due to the specificity of anionic sacran chains to adsorb trivalent metal ions and to bundle the chains.

Self-organization of cyanobacterial supergiant polysaccharides induced by lanthanide adsorption

246th National Meeting (2013)

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