The Effects And Mechanisms Of Iron And Manganese Oxides On The Electron Output Efficiency Of Clostridium

The wetland in the Yellow River Delta is formed by siltation of the sediment carried by the Yellow River,iron oxides are important metal oxides in the wetland.In recent years,iron oxides,represented by Fe3O4,have been reported to strengthen the microbial interaction,such as the direct interspecies electron transfer between electricity-producing bacteria and methanogens.However,compared with defined pure culture systems,the microbial communities and metabolic pathways in natural environment are diverse,and the electron transfer mechanisms are more complex and changeable.Little is known about quantifying the effect of Fe3O4 on interspecies electron transfer in natural environment from the perspective of electron output efficiency.Therefore,the effect of iron oxide?Fe3O4?on electron output efficiency of microorganisms in the wetland was explored in the first part.It has been reported that Clostridium spp.could potentially directly transfer electrons to methanogens.Clostridium is rich in the Yellow River Delta,and more and more Clostridia have been confirmed to belong to fermentative dissimilatory metal-reducing microorganisms with the ability of extracellular electron transfer.Therefore,there may be a close relationship between the electron output of Clostridium in the Yellow River Delta and multivalent metal oxides.In order to understand the effects and mechanisms of multivalent metal oxides on microbial electron output comprehensively and preliminarily evaluate the effects of multivalent metal oxides on microbial electron output in the Yellow River Delta,Clostridium sp.was taken as the research object to explore the effects of multivalent metal oxides on its electron output.The results are as follows.?1?The effect of iron oxide?Fe3O4?on the electron output efficiency of microorganisms in the wetland was explored.In order to realistically simulate the natural environment,unlike the single carbon sources used in previous studies,the main plant?reed?in the Yellow River Delta was used as the carbon source in this study.The result showed that the rate of methane production was increased in the presence of Fe3O4 on an hour-long timescale.The stoichiometric relationship between acetate,CH4 and CO2 and the current density measurements indicated that electron as the reducing agent to drive the CO2 reduction was the key pathway for methane production,and conductive Fe3O4 played a key role in stimulating electron transfer for methane production.Further,according to the stoichiometric relationship in electromethanogenesis,it was finally calculated that Fe3O4 increased the electron output efficiency of microorganisms in the Yellow River Delta wetland by 202.67%.?2?The impacts of iron and manganese oxides?Fe2O3 and MnO2?on DSM525's electron output efficiency were explored in the second part.We added different concentrations of Fe₂O₃ and MnO₂ to DSM 525's fermented system containing glucose.By detecting the accumulative metabolites of DSM 525,we calculated DSM525's electron output efficiency.The result showed that,the current could be detected by the microbial fuel cells inoculated with DSM 525,and the maximum current density was 0.93 mA/m².The amount of substance of Fe²⁺/Mn²⁺gradually increased.The consumption of glucose in the fermented system was increased by 9.4%and7.7%,meanwhile,acetate-producing was increased by 37.5%and 25.0%,and butyrate-producing was increased by 22.7%and 6.8%.Besides,hydrogen-producing was increased by 21.6%and 9.8%,and the calculated total electron output efficiency was increased by 24.3%and 10.8%.The pH values between control and experimental group were no significant difference.The effect of Fe²⁺on the electron output of Clostridium showed that the total electron output efficiency was increased by24.3%/10.8%when 1.35/2.55 mmol/L Fe²⁺was added,however,Mn²⁺had no promoting effect.As the concentration of Fe²⁺/Mn²⁺increased,the electron output efficiency of Clostridium decreased gradually.In conclusion,DSM 525 has the capacity for generating electricity and reducing Fe2O3 and MnO2.Addition of iron and manganese oxides could enhance DSM 525's electron output efficiency by increasing glucose consumption,buffering pH values and release of the trace elements enhancing microbial hydrogenase activity.In summary,in this thesis,the effects of iron and manganese oxides on microbial electron transfer were explored.Fe3O4 accelerated direct interspecies electron transfer in wetland soil.This study extends the research scope of direct interspecies electron transfer from defined microbial cultures to wetland soil,and quantifies the effect of Fe3O4 on microbial electron output in natural environment from the perspective of electron output efficiency,and expands our understanding of the effect of iron oxide?Fe3O4?on microbial electron output in nature.In other part of the thesis,iron and manganese oxides?Fe2O3 and MnO2?enhanced the electron output efficiency of Clostridium.This study has increased our understanding of the interaction between microorganisms and multivalent metal oxides.