Abstract
While most cyanobacteria produce soluble glycogen as the storage polysaccharide, some unicellular diazotrophs synthesize starch-like insoluble polysaccharide. In the present study, the polysaccharides were purified from Cyanobacterium sp. NBRC 102756 (MBIC 10216), Cyanothece sp. ATCC 51142, and strain CLg1, and characterized. Under scanning electron microscope, small grains of approximately 0.5 μm in diameter were observed in all preparations. Analysis by capillary electrophoresis of the debranched polysaccharides indicated the presence of long glucan chains (DP (degree of polymerization) ≥ 37) which are not found in glycogen. Using gel filtration analysis, these long chains were detected as the fraction containing B2 chains, which connect units of tandem cluster structure of the amylopectin molecule. The relative abundance of this fraction varied significantly among different strains. In addition, amylose-like linear glucan component was observed in strain CLg1. These results indicated that the structure and physicochemical properties of insoluble polysaccharides in cyanobacteria were highly similar to those of starch in plants and were variable among one another.
