Isolation Of High Efficiency Electrogenic Bacterium And Its Mechanism Of Electron Transfer

Microbial fuel cell?MFC?is an electrochemical device which can convert biochemical energy into clean electrical energy.In the MFC,anodic electrochemical active bacteria catalyze the consumption of organic substrates to complete their own metabolism.Meanwhile,some electrons are transferred to the external circuit through the anode to complete energy conversion.In this process,sewage is also purified.The electrogenic bacteria as a catalyst directly affect the efficiency of electricity generation.However,the mechanism of electron transfer in the process of electricity generation has not been clarified yet,so that there is theoretical deficiency for the regulation during the application of MFC.In this paper,four strains of electrochemical active bacterium were isolated from anode biofilm in a stable operated MFC,which was inoculated with the activated sludge of the Fourth Xi'an Municipal Wastewater Treatment Plant.The electricity generation performance and electron transfer mechanism of the most active electrochemical strain was studied.Main research results of this paper are as follows:?1?The MFC inoculated with activated sludge from the Fourth Xi'an Municipal Wastewater Treatment Plant was rapidly started up,and had a stable output voltage and good electricity generation.Its maximum power density reached 9400 mw·m^-2.Then a strain of high efficiency electrogenic bacterium,F4 was isolated through directive cultivation using iron-reducing medium from this MFC.It was identified as Klebsiella by 16SrDNA and the sequence number registed was TD665W2E016.Strain F4 is gram-negative bacillus,and its suitable growth conditions require an anaerobic environment at pH 7.0 and temperature of35°C.The MFC constructed by inoculating 20%F4 suspension had good electrical performance,and its maximum power density was 3803 mW·m^-2.?2?Evaporation and osmotic pressure had little influence on the liquid in volume of both chambers in double chamber microbial fuels.The liquid level difference between two chambers was mainly caused by biological metabolism and electroosmosis drag.In the operation of MFC,water transfer was positively related to output voltage.With the increase of output voltage,the amount of water transferred between anode and cathode increased,thus,the anode fluid level descended faster.The proton transfer rate of MFC could be calculated through the variation of liquid volume.The proton transfer rate of this system was greater than 54%,indicating that the battery had a good performance.?3?After the MFC was initiated successfully with inoculum of strain F4,a large number of electron carriers were generated by altering the anode substrate during the respiration of electrogenic bacterium which assisted the extracellular electron transfer,and could be reused to improve electricity generation efficiency.With the addition of different inhibitors,it was found that rotenone had the greatest negative effect on the oxidation peak of strain F4,which meant the ability to give out electrons was suppressed.The inhibitory effect of antimycin A was weaker than that of sodium azide.From this,it could be inferred that electrons in the intracellular transportation were mainly produced by the dehydrogenation of NADH,and then joined the Q cycle through Co Q.In the Q cycle,a part of the electrons were delivered through the iron-sulfur protein ISF transfer to the cytochrome c,and eventually to the extracellular electron acceptor.The other part of the electrons participated in the reduction of semiquinone free radicals in the Q_i-site of Q-cycle.During this process,the anthraquinones were reduced to produce Q/QH₂ and other substances,which can serve as electron carriers to assist electron transfer to extracellular electron acceptors.The discovery of extracellular and intracellular electron transport pathways had shown that the electronic transmission mode of strain F4 was mainly based on the secretion of electron mediators to assist electricity generation,and the direct contact electrode was the supplementary way transfering electrons via cytochrome c.