Bi-directional Regulation Of Electroactive Microbial Community By Antimicrobial Peptide/AuNPs Complex

Electroactive microorganisms(EAMs)are a large class of microorganisms in nature that can achieve energy metabolism through extracellular respiration.People usually combine electroactive microorganisms with electrodes for microbial fuel cells(Microbial fuel cell,MFC)to obtain electrical energy while degrading various pollutants.The power generation and pollutants removal efficiencies of mixed electroactive microbial community rely on the effective electron transfer between outer membrane proteins of electroactive electricigens.However,the slow transfer of electrons between electroactive microorganisms and with the anode interface and the weak electroactivity of the anode biofilm limit the scale-up application of MFC.In general,the modification of electrode surfaces by enhancing hydrophilic and conductive chemical groups can facilitate biofilm attachment and electron transfer between electrogenic bacteria and the interface.However,most electroactive biofilms are multilayer bacterial aggregates,and a large number of electrogenic bacteria in the outer layer cannot directly transfer electrons to the electrode surface through physical contact.Although electrogenic bacteria far from the electrode can carry out long-distance electron transport through the contact between C-type cytochrome or nanowires on their outer membranes,the limited conductivity of the outer membrane proteins of electrogenic bacteria and the doping of non-electrogenic bacteria and weak electrogenic bacteria in biofilms greatly hinder effective contact and electron transfer between electrogenic bacteria.Herein,this study developed a conductive antimicrobial peptide/gold complex,which inhibited the nonelectrogenic bacteria and promoted the electron transfer of electrogenic bacteria through the "bidirectional" regulation of the bacteria,thus improving the electrochemical activity of the bacteria and obtaining high performance MFC.The main research contents are as follows:Firstly,the antimicrobial peptide/gold complex with the best conductivity was obtained by optimizing the preparation conditions combined with antibacterial and EIS tests,and its structure was characterized.The conditions for the development of Au NPs functionalized antimicrobial peptides were optimized by screening the concentrations of linkers and antimicrobial peptides in the preparation of the antimicrobial peptide/gold complex.Combined with antibacterial experiments and EIS tests,it was proved that the antimicrobial peptide/gold complex with 2-MPA as the linker and 1 g/L Nisin concentration had the best antimicrobial properties and electrical conductivity.The antimicrobial peptide/gold complex was characterized by CD spectrum,TEM,UV-Vis,FTIR,surface Zeta potential and contact Angle,and the conductive antimicrobial peptide/gold complex was verified.Secondly,the effect of the conductive antibacterial peptide/Au NPs complex on electrogenic and non-electrogenic bacteria and the electron transfer mechanism between the bacteria expressing the outer membrane conductive protein were investigated.Through the antibacterial experiments on the antibacterial peptide/gold complex of nonelectrogenic bacteria represented by S.aureus and E.coli and the antibacterial bacteria represented by S.oneidensis,it was proved that the antibacterial peptide/gold complex had an inhibitory effect on the non-electrogenic gram-positive bacteria but did not affect the electrogenic bacteria and Gram-negative bacteria.The decolorization experiments of the bacteria after the control of the antibacterial peptide/gold complex showed that the antibacterial peptide/gold complex improved the electrochemical activity of the bacteria,and the decolorization rate of the bacteria after the control could reach 88% in24 h.Through the sedimentation test of the interaction between the antibacterial peptide/gold complex and the engineering bacteria expressing the outer membrane conductive protein,the mechanism of promoting the electrochemical activity with the electrogenic bacteria was further explored,and it was proved that the antibacterial peptide/gold complex was conducive to promoting the electron transfer between the outer membrane conductive protein and the electrogenic bacteria.Finally,the bidirectional regulation of the antibacterial peptide/Au NPs complex on the anode microbial community was studied based on synchronous generation and decolorization,and the regulation mechanism was elucidated by electrochemical testing and microflora analysis.The antibacterial peptide/Au NPs complex was applied to MFC to regulate the anode microbial community.The effect of microbial flora regulation on the electricity production and decolorization performance of MFC was studied by voltage,polarization and decolorization experiments.CV,EIS,SEM and microbial community structure characterization were used to study the regulatory mechanism of antimicrobial peptide/Au NPs complex on microflora.The results showed that the power density and decolorization rate of MFC were increased by 103% and 33%,respectively,compared with blank control MFC,and the non-electrogenic bacteria Christensenellaceae＿R-7＿group were inhibited or even disappeared.This indicated that the high conductivity and selective antibacterial properties of the antimicrobial peptide/Au NPs complex inhibited the non-electrogenic bacteria and promoted the electron transfer among the electrogenic bacteria,thus improving the electrochemical activity of the bacteria and giving the MFC a highly efficient functional microbial community.This study provides a novel approach to "bidirectionally" regulate electroactive microbial community using antimicrobial peptide/Au NPs complexes with both conductive and antibacterial properties.It opens up a new way to obtain high performance MFC by regulating the anode microbial community.The results of this study have practical guiding significance for the popularization and application of MFC.