| Exoelectrogens is a kind of microorganism with the ability of extracellular electron transfer,which can decompose organic matter and convert the chemical energy into electrical energy.The exoelectrogens exist widely in nature.As a biocatalyst of microbial fuel cell(MFC),it has a good application prospect in many fields.However,the power output of microbial fuel cells is low and the power generation capacity is weak,which limit the application of microbial fuel cells in industry.Therefore,it is an important task to screen the strains with high efficiency and strong environmental adaptability.We constructed a microbial fuel cell using marine sediment as the inoculation source in this study.After multiple cycles of enrichment,three exoelectrogens were separated and identified from the anode electrode of the MFC.The microbial fuel cell was assembled to verify the electrical activity of bacterias.It turns out that all of them had excellent electrical activity.The results of electrochemical tests showed that the power density of one of the strains reached 470 m W/m~2.We identified its phylogenetic relationship firstly.Then we found that the bacteria belonged to a species of Shewanella algae.We observed the colony morphology and explored the substrate utilization of the bacteria in this study.We investigated the electricity generation characteristics of the Shewanella algae.The results showed that the bacteria transferred electrons mainly by forming the biofilm directly contact with electrodes.The study found that the Shewanella algae can form a rich biofilm on the electrode,and the content of its electron transporter was very low compared to the biofilm.Therefore,in order to overcome the restrictive factor of insufficient content of the electric transporter,and further improve its power output capacity,we used synthetic biology strategies to enhance its extracellular electron transport efficiency,and we introduced genes related to flavin synthesis pathway,include rib A,rib C,rib D,rib E and rib H,to enhance the synthesis and secretion of flavins electron mediators,in order to increase the content of electron mediators in the MFC and enhance the extracellular electron transfer efficiency.The research results showed that after the expression of these five genes,the strain can produce more flavins electron mediators,and its flavins compound secretion amount reaches 72±4 mg/L,and its electricity generation capacity has been significantly improved.The power density of MFC reached 1120 m W/m~2,which was 2.6 times higher than before.Finally,the anode electrode material of the microbial fuel cell was optimized.In this paper,the output voltage of five electrode materials including carbon cloth,graphite felt carbon,conductive cotton,activated carbon fiber and acrylonitrile-based graphite felt were compared.The results showed that the conductive cotton electrode can produce a stronger current output.Its unique porous structure made the electrode having a larger specific surface area.It can adsorb a large number of bacterias in a short time to form a thick biofilm,shortening the start-up time of the MFC.Then we added graphene oxide as a modified electrode material to promote the formation of three-dimensional biofilm in MFC.In addition,in order to further enhance the conductivity between the cells and the carbon cloth,we used carbon nanotube materials to modify the conductivity cotton electrode.The results showed that the electrode modified with graphene oxide and conductive carbon nanotubes had greater output voltage and power.Under laboratory conditions,the output voltage reached 700 m V,and its power density reached 2900 m W/m~2.Which was 6.1 times as much as wild type Shewanella algae.In short,we selected a high-efficiency exoelectrogens through microbial fuel cell in this project,optimized its electronic mediator,enhanced its electrical activity,and explored its most suitable electrode materials,hoped to provide a reference for the application of the bacteria in the marine environment. |
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