Comparison Of Three-dimensional Excitation-emission Matrix Spectra Of Extracellular Polymeric Substances From Unicellular And Colonial Microcystis

Microcystis is the common species of cyanobacteria that can form algal bloom,and its usually contains colonial Microcystis and unicellular Microcystis was able to produce extracellular polymeric substance(EPS).Some EPS was released into medium(RPS),and some EPS enwrapped algal cells(CPS),CPS is key factor for formation of Microcystis colony.The three-dimensional excitationemission matrix spectra characteristics of extracellular polymeric substance(EPS)of unicellular and colonial Microcystis were assayed,and the influence of different light intensity.By comparison the differences between EPS of unicellular and colonial Microcystis,which may reveal the relationship of biochemical characteristics of EPS in colony formation,and can contribute to the mechanism in outbreak of cyanobacterial blooms and have the crucial significance for prevention and control of algal bloom.Investigation of the cell growth of unicellular and colonial Microcystis showed that the increase of light intensity inhibit the cell growth of unicellular,whereas promote the cell growth of colonial,when the light intensity rise from low light intensity(30 ? mol/m2/s)to middle light intensity(50 ?mol/m2/s),then to high light intensity(70 ? mol/m2/s).The production analysis of carbohydrate and protein of unicellular and colonial Microcystis indicated that with the increase of light intensity,Microcystis cells released more EPS.Besides,colonial Microcystis have a great carbohydrate and protein production than unicellular.Three-dimensional excitation-emission matrix(EEM)spectra was applied to characterize the specific compositions in EPS matrix,and all the fluorescence EEM spectra collected of unicellular Microcystis could be successfully decomposed into a 5-component modeled by PARAFAC.Component dl(Cd1)[excitation/emission(Ex/Em)=(230,270)/336 nm],Cd2(Ex/Em)=(230,270)/336 nm,Cd4(Ex/Em)=(220,270)/298 nm were attributed to protein-like substance,while Cd3(Ex/Em)=(230,270)/336 nm and Cd5(Ex/Em)=(250,340)/(420-450)belongs to humiclike substances.Colonial decomposed into a 4-component modeled by PARAFAC analysis.Component q1(Cq1)[excitation/emission(Ex/Em)=(230,270)/336 nm],Cq2(Ex/Em)=(220,280)/336 nm,Cq4(Ex/Em)=(220,270)/298 nm were attributed to protein-like substance,while Cq3(Ex/Em)=Ex/Em(240-280)/420 belongs to humic-like substances.Compared with the RPS matrix of colonial,the humic-like substances Cd3 in unicellular sharply increased with the Microcystis growth after 11 days cultivation.Pearson correlation analysis demonstrated that the correlation between tryptophan-like substance(Cdl and Cd2)in CPS fraction and Microcystis growth decreased with increasing light intensity,whereas the correlation between tryptophanlike substance(Cq1)in CPS fraction and Microcystis growth increased with increasing light intensity.Tryptophan-like substances might contribute to the UV absorption.Therefore,the increase of tryptophan-like substance in colonial Microcystis in response to the increase of light intensity might protect cyanobacteial cell against the negative UV radiation,but this anti-UV mechanis might work in the unicellular Microcystis.This may be one of the factors resulted in the better adaptation of colonial Microcystis than unicellular Microcystis.Our data in this study indicated that the EPS composition of colonial Microcystis was different from that of unicellular Microcystis.The response of growth and EPS secretion to the increasing light intensity in colonial Microcystis was different from that in unicellular Microcystis.