Chemical characterisation of the released polysaccharide from the cyanobacterium Aphanothece halophytica GR02

The released polysaccharide from the halophilic cyanobacterium Aphanothece halophytica GR02 was separated into two main fractions by anion-exchange chromatography. The major fraction consisted of glucose, fucose, mannose, arabinose and glucuronic acid. Judging from the chromatography on Sepharose 2B, the major fraction was not further fractionated, and its apparent molecular weight was above 2.0 x 10(6) Da. The minor fraction consisted of rhamnose, mannose, fucose, glucose, galactose and glucuronic acid, with traces of arabinose. Methylation and GC-MS spectrometry analyses of the major fraction revealed the presence of 1-linked glucose, 1,3-linked glucose, 1,3-linked fucose, 1,4-linked fucose, 1,3-linked arabinose, 1,2,4-linked mannose, 1,3,6-linked mannose, 1-linked glucuronic acid and 1,3-linked glucuronic acid residues. The major fraction was thought to originate from capsular polysaccharide. The released polysaccharides, obtained from cultures at different age of culture, showed no striking variations in the monosaccharide composition and the relative proportions of the monosaccharides. However, the proportions of galactose and rhamnose in the released polysaccharides, obtained from cultures under different salinity, were significantly different. The released polysaccharide also exhibited gelling properties and strong affinity for metal ions.