Reactive Mechanisms Between Microorganism & Extracellular Polymeric Substance (EPS) And Heavy Metal In Water Columns

Extracellular polymeric substance(EPS) secreted by microorganism plays an important role in pharmacy,cultured milk and wastewater treatment in environment. In order to understand the combining mechanism between microorganism & its extracellular polymeric substance and heavy metals.the study uses a stimulating method in laboratory to gradually understand at large relationship of three aspects as follows:physiological response of microorganism to heavy metal stress,changing EPS property induced by heavy metal and the combining mechanism between EPS and heavy metals.The results show in the following.Firstly,existing Ca²⁺ can decrease stress of heavy metal Cd on algal cells,and protect cells from more damage,which can be attributed to protecting effect of calcification layers triggered by bio-calcification.Secondly,slight Cu can induce Synechocystis sp.to produce more protein-like and soluble microbial product-like EPS that is MW>14.000Da.And humus in EPS is not from secretion of microorganism.but decaying and decomposing microorganism is its source.Finally,the results about combining mechanism between heavy metal Cd and two EPSs show that an obvious quenching effect of LB triggered by Cd concentration less than 1×10^-4 mol·L^-1 can be observed at pH value 4.The phenomena that was quenched at lower pH value was not only related with the protonation effect of fluorophores.but also linked with the change of combining sites between Cd and protein-like.In addition.for the analysis of further three-dimensional fluorescence spectrum,fluorophores of protein-like in LB have character of singleness,whereas fluorophores of TB have a characteristic of diversity.At pH 10 quenching of fluorescence peaks of protein-like in LB and TB are resulted from two aspects,on the one hand,it was related with the production of EPS-Cd complex,and on the other hand it can be attributed to colliding quenching between fluorescence molecules.In the study.theoretical innovation on fluorescence titration is not only exhibited but also these conclusions will help us to understand the self-purification of water columns in heavy metals.