The Role Of Extracellular Polymeric Substances In Extracellular Electron Transfer Of Electrochemically Active Bacteria

Microbial electrochemical systems(MES)use electrochemically active bacteria(EAB)as catalyst to catalyze the redox reaction on electrode surface,which show great potential for reclamation and energy recovery.Extracellular electron transfer(EET)of EAB is the prerequisite for function realization of MES.In most of researches about EET,bacteria was thought to realize EET by contacting with extracellular electron acceptor directly and nakedly,however,in real environment,most of bacteria in biofilm or aggregates wrapped by extracellular polymeric substances(EPS),so,it is imperative to analyze the role of EPS in EET.In this study,Shewanella oneidensis MR-1(Gram-negative),electrochemically active model bacteria,the two strains WS-XY1(Gram-positive)and Ps(fungi)which were isolated from microbial fuel cell were chosen to address the roles of EPS in EET processes by electrochemical method.Main results are summarized as follows:1.Heating method was selected for EPS extraction of MR-1,WS-XY1 and Ps.According to flow cytometry data,38,45 and 55 ? were chosen as the optimum extraction tempreture for MR-1,WS-XY1 and Ps,respectively.After extracting EPS at optimum extraction tempreture,EPS were removed effectively from bacterial surface,meanwhile,bacteria still keep high activity.2.Comparing the EET of MR-1 before and after EPS extraction,the result shows that EET ability of MR-1 was improved after EPS extraction.Before EPS extraction,outer membrane c-type cytochromes and flavins are the main substances involved in EET,after EPS extraction,the flavin/MtrC combination and outer membrane c-type cytochromes are the main substances involved in EET.For WS-XY1 and Ps,the datas show that EET ability of WS-XY1 and Ps was improved after EPS extraction.3.Comparing the differential pulse voltammetry(DPV)datas of the three different strains(Gram-negative,Gram-positive,fungi)before and after EPS extraction,the results show that DPV peaks potential of MR-1 was changed after EPS extraction,this means that the substances involved in MR-1 EET was also changed.However,for WS-XY1 and Ps,DPV peaks potential was changed barely after EPS extraction,presumably,the substances involved in WS-XY1 and Ps EET was not changed.4.For the three kinds of EABs,there is a certain degree of improvement in EET ability after EPS extraction,this means that EPS inhibit EET in some degree.