Flocculating activities of polysaccharides released from the marine mat-forming cyanobacteria Microcoleus and Lyngbya

Mat-forming cyanobacteria of the genera Microcoleus and Lyngbya were isolated from the Tainan Saltworks, China. The released polysaccharides (RPSs) from the 2 cyanobacterial isolates flocculated kaolin clay from suspensions, and this flocculating activity decreased with increasing pH from 3 to 10.5. The flocculating activities increased with increasing metal ion concentrations and reached plateaus when the concentrations of monovalent cations (Na(+) or K(+)) and divalent cations (Mg(2+) or Ca(2+)) increased to 0.4 and 0.2 mol l(-1), respectively. Compared with the previously reported data about the flocculating activities of exopolysaccharide from the freshwater cyanobacterium Phormidium J-1, the presence of higher concentrations of metal ions was required for the flocculating activities of the RPSs from the 2 marine cyanobacteria studied here. The production of extracellular bioflocculants by the benthic cyanobacteria could be of considerable importance in the flocculation and sedimentation of clay particles in brines, which in turn would allow light to penetrate to the sediment-water interface.