Study On The Role Of EPS In The Removal Of Heavy Metal Cd²⁺ By Desulfovibrio Desulfuricans

In this paper, extraction method of extracellular polymeric substances（EPS） from the sulfate reducing bacteria （SRB） of Desulfovibrio desulfuricanswas optimized and their role in the removal of heavmetal was investigated.The results were listed as following:（1） The extracting efficiencies of EPS from Desulfovibrio desulfuricansusing ethylene diamine tetraacetic acid disodium salt （EDTA）, cationexchange resin （CER）, NaOH, H2SO4, heating and sonication were compared.Results showed that heating was most effective in extracting EPS. Thecarbohydrate, protein and nucleic acid in the EPS solution were4.83,12.62and4.80mg/g dry cells, respectively. UV–visible spectrum of the EPSextraction suggested that few cells were destroyed and lysis did not occur.（2） The result of researching D. desulfuricans growth cycle show that:order the stages of SRB growth cycle is: adaptation period （0-24h）,Logarithmic growth period （24-60h）, Stabilization period （72-96h） and thendecline period; the main ingredients of extracellular polymeric arepolysaccharides and proteins,but also a small amount of a nucleic acid. TheEPS components and contents is changed in D. desulfuricans growth, littleEPS in adaptation period, then its amount is rising and reaches the maximumat84h; in decline period of SRB, the conjugated EPS content increasedcompared to the solubility EPS.（3） The experiment have research impaction of diffirent concentrations ofheavy metals (On behalf of Cd²⁺) on the growth of D. desulfuricans and thechanging of EPS component and content, the result show that: test strains,maximum tolerated concentration of Cd²⁺is28.0mg/L, When theconcentration of Cd²⁺less than28.0mg/L, sulfate-reducing bacteria is active,removal rate of Cd²⁺reached99.0%. Protein is the main component of EPSwhich produced by D. desulfuricans, and Cd2+have promoted the secretion ofprotein, EPS has a positive effect on Cd2+removal, It’s contribution rate ofthe removal can reach to10.0%.（4） Through the study f Cd²⁺on the growth of D. desulfuricans, we knowthat: the main existing from of Cd are dissolved Cd²⁺、CdS （Precipitation state） and complex state Cd which present in microorganisms. By study SEM-EDScharacterization we found that bacteria extracellular material can combinedwith Cd²⁺and S2-to produce bio-complex, to the role of fix Cd²⁺, so EPSplays a very important role in removal of Cd²⁺.