Exopolysaccharide from cyanobacterium Synechocystis aquatilis – production rate, chemical characterization and biological testing

Abstract

Cyanobacteria are a very abundant source of structurally diverse polysaccharides which are characterized by a great variety in both number and type of constitutive monosaccharides (acidic and neutral sugars) [1]. The strain Synechocystis aquatilis Sauvageau B90.79 is a unicellular cyanobacterium (order Chroococales, family Chroococaceae) which was found to produce and release high amounts of polysaccharides (so called released polysaccharides, RPSs) into its watery environment during cultivation. After 60 days of 8-L-batch cultivation, the average yield of the RPS was 0.5g/L and hence the mean RPS productivity was 8mg L-1 d-1. According to chemical analysis, the S. aquatilis RPS belongs to the group of sulfated fucose-rich polysaccharides: it was mainly composed of arabinose (45%) and fucose (47%) and had a degree of sulfation of 0.43. Biological testing of the RPS revealed a moderate anticoagulant activity of less than 10% compared to the reference compound unfractionated heparin. However, distinctive effects on the complement activation were observed: its inhibitory effect on the classical pathway of complement activation was 600fold stronger than that of unfractionated heparin, whereas that on the alternative pathway of complement activation was 2–3fold weaker. The results indicate that this biotechnologically producible RPS represents a specifically acting complement modulator.