The Effects And Mechanisms Of Conductive Materials On Physiological Activities Of Methanogens And Geobacter

Iron???reducing bacteria?IRB?and methanogens distribute in the wetland ecosystem,involving biogeochemical carbon?C?and iron?Fe?cycle process.Extensive studies have suggested that conductive materials,such as magnetite,activated carbon and carbon cloth,are conducive to direct interspecies electron transfer?DIET?between IRB and methanogens,which could facilitate methane production.Most studies focus on the effect mechanisms of conductive materials on electron transfer and methane production via pure culture.While,it is uncertain whether these findings are appropriate for on environmental samples.In this study,to elucidate the effects of conductive materials on the physiological activities of IRB and methanogens,we investigated the effect and mechanisms of carbon cloth on methanogenic processes in wetland soil.In the meantime,the ability of iron???reduction and electrochemical activity as well as chloramphenicol degradation ability of IRB were evaluated in the existence of non-conductive microplastics and carbon cloth,respectively.To clarify the effects and mechanisms of conductive materials on activities of methanogens and Geobacter is conducive to enhance the further understanding of their contribution to microbial mediated C,Fe biogeochemical cycles process.Moreover,the findings about the effects of microplastics and antibiotic?CAP?on activities of IRB provide theoretical support the protection and sustainable development of the coastal wetland ecosystem in the Yellow River delta.The main conclusions are summarized as follows:?1?In this study,the effect of carbon cloth,as a representative of conductive carbon material,on methane production with incubated wetland soil was investigated.Carbon cloth significantly promoted methanogenesis.With the application of electrochemical technology,calculation of the apparent electron transfer rate constant showed that carbon cloth significantly increased electron transfer rate(k_app)compared with the control experiment,from 0.0017±0.0003 to 0.0056±0.0015 s^-1.Results obtained from both stable carbon isotope measurements and application of specific inhibitor?CH₃F?for acetoclastic methanogenesis indicated that carbon cloth obviously promoted acetoclastic methanogenesis instead of CO₂ reduction.High-throughput sequencing showed that carbon cloth did not appear to alter the community structure of methanogenic archaea to any significant extent.Mobilitalea spp.and Pseudobacteroides spp.were the most abundant bacteria in both treatment groups and Methanosarcina spp.,showed the highest abundance of methanogens.?2?The effects of two typical microplastics,PBAT and PVC,were explored on the activity of G.metallireducens GS15 with ferrihydrite or ferric citrate as respective electron acceptors.The results showed that the iron?II?contents in PBAT and PVC treatment groups were 16.79 m M and 6.81 m M,respectively at the end of the experiment.Compared with PBAT treatment group,SEM-EDS revealed that merely small amount of iron-containing products covered the surface of PVC.Moreover,PBAT and PVC could both retard the electroactivity of G.metallireducens GS15 at the beginning of microbial fuel cell operation.Based on the results above,microplastic PVC might exhibit potential inhibition of the iron cycling process driven by G.metallireducens GS15 with ferrihydrite as the terminal electron acceptor.Geobacter spp.have evolved different mechanisms for electrons transfer with various iron???oxides.Compared with insoluble iron???,microbes are prone to use soluble iron???.Hence,the effect of PVC on ferrihydrite reduction was more obvious.?3?As typical iron reduction bacteria,Geobacter sulfurreducens PCA was adopted to remove chloramphenicol?CAP?in the presence of carbon cloth.Cyclic voltammograms and chronoamperometry highlighted a higher peak current for CAP reduction by G.sulfurreducens PCA compared to the control without bacteria.The results showed that initial CAP concentration,temperature,the conductive material and cathode potential could influence the degradation efficiency of CAP.Microbial activity decreased with the increase in CAP concentration.There was obvious inhibition effect on Geobacter activities when the initial concentration of CAP was greater than 20 mg/L.In the meantime,the inhibition effect of CAP was attenuated with the increase of temperature and the addition of conductive carbon cloth.In addition,G.sulfurreducens PCA as a typical electroactive microorganism could reduce CAP with cathode as the terminal electron donor.Applied voltage had a significant influence on CAP reduction.The lower the cathodic potential,the higher CAP reduction efficient was achieved.The degradation rate of CAP was further improved with the addition of sodium acetate at-0.6 V vs SHE.