Biosynthesis of a sulfated exopolysaccharide, synechan, and bloom formation in the model cyanobacterium Synechocystis sp. strain PCC 6803

Extracellularpolysaccharides of bacteria contribute to biofilm formation, stress tolerance, and infectivity. Cyanobacteria, the oxygenic photoautotrophic bacteria, uniquely produce sulfated extracellular polysaccharides among bacteria to support phototrophic biofilms. In addition, sulfated polysaccharides of cyanobacteria and other organisms have been focused as beneficial biomaterial. However, very little is known about their biosynthesis machinery and function in cyanobacteria. Here, we found that the model cyanobacterium, Synechocystis sp. strain PCC 6803, formed bloom-like cell aggregates embedded in sulfated extracellular polysaccharides (designated as synechan) and identified whole set of genes responsible for synechan biosynthesis and its transcriptional regulation, thereby suggesting a model for the synechan biosynthesis apparatus. Because similar genes are found in many cyanobacterial genomes with wide variation, our findings may lead elucidation of various sulfated polysaccharides, their functions, and their potential application in biotechnology.

Biosynthesis system of Synechan, a sulfated exopolysaccharide, in the model cyanobacterium Synechocystis sp. PCC 6803

Extracellular polysaccharides of bacteria contribute to biofilm formation, stress tolerance, and infectivity. Cyanobacteria, the oxygenic photoautotrophic bacteria, uniquely and widely have sulfated extracellular polysaccharides and they may utilize the polysaccharides for survival in nature. In addition, sulfated polysaccharides of cyanobacteria and other organisms have been focused as beneficial biomaterial. However, very little is known about their biosynthesis machinery and function in cyanobacteria. Here we found that the model cyanobacterium, Synechocystis sp. PCC 6803, formed bloom-like cell aggregates using sulfated extracellular polysaccharides (designated as synechan) and identified whole set of genes responsible for synechan biosynthesis and its transcriptional regulation, thereby suggesting a model for the synechan biosynthesis apparatus. Because similar genes are found in many cyanobacterial genomes with wide variation, our findings may lead elucidation of various sulfated polysaccharides, their functions, and their potential application in biotechnology.

Preparation of a sulfated exopolysaccharide (S-EPS) from Ophiocordyceps sinensis fungus and its antioxidant effects

Sulfated exopolysaccharides have been well-known to enhance biological activities. Exopolysaccharide (EPS) produced by Ophiocordyceps sinensis fungus is a source of natural compounds. The aim of our study is to improve the EPS biological activities by its sulfated modification using the chlorosulfonic acid (CSA)-pyridine (Pyr) method. The appropriate conditions of the sulfation reaction were explored, including CSA/Pyr ratio (v/v) of 1:3 and 6h. The degree of substitution (DS) of S-EPS11 was the highest (DS = 1.59). The total contents of polysaccharides and SO42- of S-EPS11 were 52.25% and 47.15%, respectively. Besides, the FT-IR spectra analysis indicated the presence of CO-S (peak of 815 cm-1) and S=O (peak of 1129 cm-1) stretching vibrations, while the natural EPS did not appear. Importantly, OH• and ABTS• radical scavenging potential of S-EPS11 significantly increased compared with those of the natural EPS. Together, we successfully generated sulfated EPS extracted from O. sinensis fungus which enhanced antioxidant activities of natural EPS.