| Due to the worldwide shortage of fossil fuel and the extreme weather caused by global warming,the cellulose biomass has received an increasing attention as an alternative energy source.Cellulose biomass has the characteristics of wide distribution,huge reserves,low price,and renewability.Microbial fuel cell（MFC）with cellulosic biomass as the substrate is an effective way to alleviate energy crisis and environmental problems in the future.In this dissertation,rumen fluid and domestic sewage were used as the inocula to enrich and screen out strains that can efficiently degrade cellulose and glucose respectively,and then established a ternary system with Geobacter sulfurreducens PCA.After using MFC to screen out the optimal interaction system,electrochemical analysis,substrate degradation and metabolite analysis were used to elucidate the main interactions between strains and the limiting factors of electricity production.（1）Two single strains named J1 and J2（cellulose and glucose degradation bacteria,respectively）were isolated by repeated plate streaking and identified using PCR through 16S r DNA sequencing.By comparison with sequences in Gen Bank,the strain J1 belongs to the genus Paenibacillus and is related to Paenibacillus lentus CMG1240,with a similarity of98.04%,and strain J2 belongs to the genus Klebsiella and is related to Klebsiella pneumoniae subsp.rhinoscleromatis ATCC 13884,with a similarity of 99.30%.（2）By analyzing the physiological and biochemical characteristics of strain J1 and J2,it was found that strain J1 is a facultative anaerobe with an optimum temperature of 37°C and an optimum p H of 6.5.Besides,strain J1 can use carboxymethyl cellulose（CMC）,cellobiose and glucose but cannot utilize sodium acetate.Strain J2 is also a facultative anaerobe with an optimum temperature of 37°C,an optimum p H of 7,and is incapable of utilizing cellulose and sodium acetate,but it can rapidly metabolize ce llobiose and glucose.In addition,strain J1 and J2 did not possess electrochemical activity.（3）This research demonstrates the design and investigation of a defined ternary culture of strain J1,J2 and G.sulfurreducens PCA as biocatalysts for CMC-derived electricity production.The maximum current density of the ternary culture achieved in half-cell experiments was 621±23μA cm-2 and the maximum power density reached 1146±28 m W m-2 in two-chamber MFC.（4）Based on cellulose degradation and metabolites analysis,these three bacterial species could efficiently transfer essential metabolites to form a step-by-step-feeding microbial consortium for power generation.Strain J1 efficiently fermented CMC into cellobiose and glucose,while strain J2 can timely convert cellobiose and glucose into varies organic acids including acetate acid for G.sulfurreducens PCA to use as a carbo n source in conjunction with anode reduction.（5）Confocal images of G.sulfurreducens PCA and the ternary culture biofilm on carbon electrode surface after 96 h operation support the similar crossing section thickness at approximately 20μm.However,scanning electron micrographs of CMC-fed ternary culture biofilm showed heterogeneous cell morphologies,suggesting that strain J1 and J2 might also adhere to the electrode.Besides,the voltammograms under substrate exhaustion were recorded on G.sulfurreducens PCA and the ternary culture biofilm at different scan rates.The results showed that the catalytic current of the ternary culture biofilm is more hindered by electron transfer process rather than diffusion,indicating the existence of more diffusion substances including protons or electron transfer mediator（ETM）in co-culture biofilm than that in G.sulfurreducens PCA biofilm.Furthermore,these diffusion substances produced by the ternary system could only efficiently accelerate the electron transfer,but did not contribute to CMC degradation. |
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