Investigation On The Exopolysaccharides (EPS) From Three Cyanobacterial Strains And Identification Of These Strains

Three cyanobacterial strains isolated from marine water in China can release an amount of Exopolysaccharides (EPS) to the culture medium. The optimal culture medium components (NaCl concentration and MgSO4 concentration) and culture conditions (temperature and light intensity) for Exopolysaccharides production by the three strains were investigated using"one-variable-at-a-time"method. The results show that the optimal medium components were:A104: 60 gL-1NaCl, 0.6 gL-1 MgSO4,A109: 40 gL-1 NaCl, 0.7 gL-1 MgSO4, A115: 30 gL-1NaCl, 0.8 gL-1 MgSO4. and the optimal culture conditions were: A104: 28℃, 3600 Lux; A109: 28℃, 2700 Lux; A115: 28℃, 3600 Lux. Under the optimal medium components and culture conditions ,the strains A104, A109, A115 reached 8.57 g L-1,7.53 g L-1 and 6.98 g L-1 of EPS on 12 day,9 day,11 day, respectively.Ethanol was used to precipitate the soluble exopolysaccharides from culture supernatant, protein and other small moleculr impurity of the crude exopolysaccharides were removed using Sevag method and dialysis, respectively. After purification of crude exopolysaccharides by gel filter method, purified exopolysaccharides were found to be single molecular mass polysacchrides. The molecular mass of the three exopolysaccharides were 25kD, 38kD and 46kD. Sulfate and uronic acid were not found in these exopolysaccharides. Monosaccharides components of the exopolysaccharides were analysised using TLC.The results of identification of the strains based on morph- ological analysis were not consistent with the results based on 16SrRNA gene sequence analysis. So, further investigation should be done using other identification methods.