Study On Strengthening Strategies For Electron Uptake Capacity Of Cathodic Electroactive Microorganisms

Microbial electrosynthesis?MES?is a kind of devices in which cathodic electroactive microorganisms?CEAM?obtain electrons from solid electrodes to reduce CO₂ or other oxidized substances into extracellular organic substances or reduced inorganic substances.MES has the advantages of saving the cultivated land and utilizing green energy.Therefore,it has broad application prospects in the fields of synthetic chemicals,greenhouse gas reduction and agricultural environmental remediation.However,inefficiency of MES limits its scale enlargement and commercial application.Electroactive biofilms?EAB?are formed when CEAM exchanges electrons with solid electrodes.The formation of cathodic EAB is more difficult and time-consuming than that of anodic EAB,which is also a key technical difficulty for MESs.At present,research on improving the MES performance mainly focuses on the modification of cathodic materials,the design of reactors and the selection of CEAM.However,few studies are focused on the modification of the CEAM and the biofilm formation process.Based on the above,this paper focuses on the CEAM in MES with electrochemical and molecular biological methods.Aims of this study are to explore:1)whether the penicillin can promote the electron uptake capacity and organic acid synthesis efficiency by increasing the cell permeability of Gram-positive Moorella thermoautotrophica;2)whether the rhamnolipid can improve the cell permeability of Gram-negative Sporomusa ovata to promote the acetate synthesis efficiency and 3)whether acyl-homoserine lactones?AHL?can accelerate the start-up of Geobacter soli GSS01 cathodic EAB.Main results are as follows:?1?When?30 mg/L penicillin was added,the cell permeability was doubled,and the electron uptake per biomass was 1.84 times that of the control,while formate and acetate production rates per biomass were 1.96and 2.23 times those of the control,respectively.Coulombic efficiencies increased from 73%±3%to 88%±3%,indicating that the increasing cell permeability can enhance the electron uptake capacity and chemical product synthesis rate of Gram-positive bacteria in MES.Enhanced cell permeability caused higher redox activities of outmost cytochrome and increased the release of redox electron shuttles,both of which were the main reasons of the enhanced extracellular electron uptake and product synthesis.?2?When 50 mg/L rhamnolipid was added,the cell permeability of S.ovata was increased,and the electron uptake per biomass was 2.6 times of that of the control.Acetate production rates per biomass were 2.83times of that of the control.The electrochemical in situ FTIR spectra data indicated that the redox activity of the protein relating to electron transfer was improved with rhamnolipid addition,which was beneficial to the uptake of extracellular electrons and the electrosynthesis performance.?3?AHL advanced the start-up of G.soli cathode EAB.Cathodic biofilms could be directly started-up in the cathode chamber with AHL addition.The start-up time was shortened to 50%of the control.After the biofilm formation,the electron uptake capacity of the G.soli was enhanced with AHL addition,and the nitrate reduction rate was more than twice of that of the control.In the cathode-associated G.soli EAB with AHL addition,the biomass and cell viability were increased,the abundances of extracellular polymeric substance compositions especially proteins and polysaccharides were increased,and the redox activities of the outermost proteins were enhanced.Thus,the EAB performance was promoted in the presence of AHL.