Exopolysaccharides Of Colonial And Unicellular Microcystis

Cyanobacteria bloom brought great harm to public health and environmental safety,Microcystis spp.are the most common bloom-forming cyanobacteria.Microcystis always occurs in a colony under natural conditions,but exists mainly as single cells in axenic cultures in the laboratory.Microcystis spp.produce large amounts of exopolysaccharides(EPSs)including capsular polysaccharides(CPSs),which form mucilaginous matrix around the cells,and water-soluble released polysaccharides(RPSs).To understand their ecophysiological roles in cyanobacterial bloom,more information on biochemical characterization of EPS is urgently needed and three colonial strains(M.wesenbergii H4,M.firma H54,M Aeruginosa H78)and three unicellular strains(M.Wesenbergii H2,M.Firma H43,M.Aeruginosa H177)were choosed.The chemical composition and biochemical characteristics of EPS were assayed,and their differences between colonial strains and unicellular strains were compared.Furthermore,the differences of chemical composition between RPS and CPS for the same strain were assayed.Those will help understanding the influence of biochemical characteristics of EPS in colony formation,and can contribute to the mechanism of conversion between colonial strains and unicellular strains.Furthermore,it may have the important significance for prevention and control of algal bloom.All the six Microcystis strains were maintain stable colony or unicellular form with continuous ventilation cultivation in 3 L conical flask.The comparative study of chemical characteristics of EPSs from three colonial strains and three unicellular strains showed that(1)the EPS production of colonial Microcystis(0.114?5.47pg.cell-1)was higher than unicellular Microcystis(0.059?0.473pg.cell-1),and higher in RPSs(0.223?5.47pg.cell-1)than in CPSs(0.059?1.25pg.cell-1)for each strain;(2)all the EPSs were containing two kinds of acidic monosaccharides(glucuronic acid,galacturonic acid)and 5 to 7 kinds of neutral monosaccharides(glucose,mannose,galactose,arabinose,xylose,fucose and rhamnose);(3)the hydrophobicity of colonial strains(31.6%?66.4%)appeared strong,while the unicellular stains had no hydrophobicity property;(4)uronic acid,acetate and sulfate groups were present in all EPSs,all the RPSs contained pyruvate,and the pyruvate content of RPS in colonial strains(0.4%?5.7%)was higher than in unicellular strains(0.3%?0.9%)overall.The acetate content was higher in CPSs(2.0%?4.9%)than in RPSs(0.7%?1.5%)for each strain,and higher in CPSs of colonial strains(4.1%?4.9%)than in CPSs of unicellular strains(2.0%?3.2%).The content of sulfate group was higher in CPSs(5.5%?13.8%)than in RPSs(3.7%?7.3%)for each strain.The uronic acid content in CPSs(1.2%?4.3%)was lower than in RPSs(2.4%?24.7%)for each strain.The chemical characteristics of EPS were discussed with respect to the solubility of EPS in water,their roles in colony formation and their ecological roles in the aquatic environments.It was thought that among these biochemical characteristics,acetyl substitution might be an important factor affecting the ecophysiological roles of EPS in cyanobacterial bloom.