Studies On Pb And Cd Adsorption By Exopolysaccharide And Extracelluar Protein Of Natural Biofilm

In natural aquatic environment ,the surfaces of solids(rock,sediments, suspended particles etc.) are mostly covered with biofilmswhich play an important role in metal adsorption onto solids .Themain compositions of biofilms are bacterial cells and extracellularpolymers produced by bacteria. Because extracellular polymersexist a large number of negative charged functional groups, theycan't only exchange ions but also contact with metal ions , andcombine with the heavy metals selectively.Though different extracellular polymers'compositions existdifference because of the influence of environment and othercondition factors, they consist mainly of exopolysaccharides ,extracellular protein, nucleic acids , and lipids etc. exopolysaccharidesand extracellular protein predominate in these ingredients, andthe ratio of exopolysaccharides to extracellular protein varies aboutfrom 0.2 to 5.Some researchers have found that biofilm components havedifferent contribution to mental adsorption onto biofilm. With alaboratory biofilm reactor system and controlled laboratoryconditions , Nelson et al. reported extracelluar polymer constitutedup to 80% of total biofilm organic material (based on chemicaloxygen demand), and its specific binding capacity for lead was threetimes higher than that of bacterial cells. But up to now , theextracelluar polymer components'binding capacity for heavymentals is less known. So it is very important to continue theresearch work. In this study, the extracelluar polymer's main components ─exopolysaccharides and extracellular protein contributing to theadsorption of lead and cadmium were investigated. The biofilm wascultured in the condition of laboratory, and the water of which wastaken from Changchun South Lake. The superiority bacteria ofbiofilm was obtained after purified, then it was put into culturesolution at the condition of 2 day and 28~30℃for enlarge culture inculture box. The glucose , Cl-and SO4 2-in the culture medium wereremoved from culture solution through dialysis, now only superioritybacteria and its exopolymer were left in the culture solution. The next step, they was separated through high speed centrifugalmethod, the bacteria cells(precipitates) at the bottom of centrifugaltube were discarded, and the supernatant liquor was extracelluarpolymer solution. The powdered ammonium sulfate was put into thesupernatant slowly, the extracellular protein were precipitated,whichwere dissolved in buffer solution(pH 7.8),then dialyzed, washed bydeionized water , and freeze-dried. The filter liquor which theextracellular protein had been isolated, was dialyzed andfreeze-dried ,then dissolved in deionized water, 90% ethanol was putinto ,the exopolysaccharides were precipitated through centrifugation,...