Exopolysaccharides Of Colonial Microcystis And Their Attached Bacteria

Microcystis is the common species of cyanobacteria that can form algal bloom,and it usually contains colonial Microcystis and unicellular Microcystis.Microcystis was able to produce exopolysaccharides(EPS).Some EPS was released into the medium(RPS),and some EPS enwrapped algal cells(CPS).CPS is the key factor for the formation of Microcystis colony.The chemical composition and biochemical characteristics of exopolysaccharides of five strains of Microcystis(NO.16,NO.50,N0.69,NO.129 and NO.183)were assayed.Comparative analysis of biochemical characteristics of exopolysaccharides from different Microcystis strains may reveal the influence of biochemical characteristics of EPS in colony formation,and can contribute to the mechanism in utbreak of cyanobacterial blooms and have the important significance for prevention and control of algal bloom.The colony of all the five Microcystis strains were cultured in 100 mL conical flask.After continuous ventilation cultivation in 3 L conical flask,only NO.16,NO.69,and NO.183 maintain colonial form,while most cells of NO.50 and N0.129 became unicellular form.The colonial area size of 16,69,and 183 was among 8071.1～20168.0μm2.Exopolysaccharide production was the main difference between colonial Microcystis and unicellular Microcystis.The production of colonial Microcystis was greater than unicellular Microcystis,and the RPS yield were greater than the CPS.Production of CPS of colonial Micocystis was among 0.777～1.707 pg-cell-1,and production of RPS was among 5.227～8.092 pg·cell-1.Production of CPS of unicellular Microcystis was about 0.068 pg·cell-1,and production of RPS was among 0.297～0.403 pg·cell-1 This paper used the method of gas chromatography and high performance liquid chromatography to analyze neutral monosaccharide composition and acid monosaccharide composition of exopolysaccharides,and results showed that the exopolysaccharides(CPS and RPS)from Microcystis contained 5～7 kinds of neutral monosaccharides(rhamnose,fucose,xylose,mannose,glucose arabinose and galactose)and glucuronic acid.Exopolysaccharides of Microcystis all contained uronic acid and acetate,and the content of acetate in CPS was more than in RPS,but the content of uronic acid in RPS was more than in CPS.Acetate content in CPS was among 2.7～9.5%,and acetate content in RPS was among 0.5～2.1%.Uronic acid content in CPS was among 1.0～2.1%,and uronic acid content in RPS was among 1.9～6.2%.Pyruvate content in CPS was among 0～3.8%,and pyruvate content in RPS was among 0～6.3%.Sulfate content in CPS was among 4.9～8.2%,and sulfate content in RPS was among 3.5～7.2%.The protein content in CPS was higher than in RPS.Protein content in CPS was among 9.5～14.1%,and protein content in RPS was among 4.3～8.1%.Colonial Microcystis had strong hydrophobicity which is among 63.1～81.6%.A large number of attached bacteria exist in EPS of colonial Microcystis,and they may produce exopolysaccharides to influence colony formation.In twenty-eight species isolated from Microcystis,Rhizobium could make medium thicker and had high production of exopolysaccharides,but other attached bacteria had low production of exopolysaccharides.So RPS of Rhizobium was selected to do further analysis.The production of RPS was 278.53μg/mL.RPS of Rhizobium didn’t contain uronic acid,and it mainly consisted of three kinds of neutral monosaccharides which were respectively glucose(83%),mannose and galactose.Acetate,pyruvate,sulfate and protein content in RPS of Rhizobium was 4.0%,5.8%,2.7%,6.3%.RPS of Rhizobium didn’t have emulsifying activity and flocculation activity,but it had low clay-dispersing activity.RPS of Rhizobium had good water solubility and that was different from EPS of Microcystis.The charateristics of exopolysaccharides between Rhizobium and Microcystis had obvious difference and played different roles in the process of colony formation of Microcystis.And EPS of Microcystis had palyed more important role in colony sheath and colony formation.