Isolation And Identification Of Symbiotic Bacteria In Slugs And Application In Microbial Fuel Cells

The increasing population and fast increased demand for energies result in rapid consumption of non-renewable fossil fuels and serious environmental pollution.The development of clean and sustainable energy technologies has become very critical and urgent.Microbial Fuel Cell(MFC)is a kind of clean energies,which utilizes the physiological function of microorganisms to metabolize various substrates and microorganisms serves as catalysts to promote the degradation of substrates in MFC for harvesting electricity.In particular,the application of MFC in water pollution treatment has specific significance because it treats the pollut wastes while producing energy for a sustainable recycle,and thus it has received great attention in research and development for its potential broad applications.As discussed above,the performance and characteristics of MFC should be closely related to the physiological characteristics of the microorganisms used and often are mostly dependent on the bioelectrochemical activity of the microbes.The large and diverse microbial populations in nature provide us a convenient and plentiful sources of microbes.In particular,the microbial population in animals is rich in diversity,and the special physiological habits of some animals are even related to the special physiological processes of the microorganisms symbiotic in their bodies.Therefore,isolation and screening of symbiotic microorganisms in animals with good bioelectrocatalytic activity for microbial fuel cells is a good research direction to explore high performance MFCs.This studies were focused on searching good bacteria for MFC biocatalysts.The original bacterial flora was obtained from a slug(captured from Chongde Lake,Southwest University of Beibei District,Chongqing)by aseptic manipulation,and recorded as KY-2 bacterial flora.Specific bacteria were isolated,identified and finally tried in MFC for their electrocatalytic behaviors.This thesis work mainly include the following parts:(1)In this study,symbiotic microflora in small animals was selected as the source.After screening,bacterial flora with higher electrical activity was screened from slugs,named KY-2.The microbial flora can enrich bacterial biofilm on the anode of microbial fuel cell in the process of power generation.Moreover,the morphology of bacteria in the SEM image of the anode biofilm and the single colony of KY-2 bacteria growing in the LB solid culture dish can be seen that there are many kinds of bacteria in the bacterial flora,but only one form of bacteria has the highest appearance rate.The macrogenomic analysis of KY-2 original flora sample,MFC double-chamber full-cell discharge anode solution sample and carbon cloth anode sample with biofilm after MFC double-chamber full-cell discharge confirmed that the bacteria with the highest rate of appearance were Bacillis bacteria.And through the analysis of the bacterial abundance(the proportion of total bacteria)obtained from the macrogenomics of the three samples,it was concluded that the Bacillis bacteria played a dominant role in the process of KY-2 power generation.(2)KY-2-22 was identified by isolating the bacteria with the highest rate of appearance.Through the identification of 16S-rDNA bacteria and the construction of phylogenetic tree of its gene,it is proved that KY-2-22 strain belongs to Bacillis,and it is closest to MH061189.1 Proteobacteria bacterium strain B154 strain in phylogenetic tree.In addition,by comparing the power production capacity and electrochemical behavior of KY-2-22 strain and KY-2 colony,it was found that the trend of KY-2-22 strain was highly consistent,and the performance of KY-2-22 strain was better than that of KY-2 colony.By analyzing the electrochemical characterization of KY-2-22,it is concluded that the electrochemical behavior of KY-2-22 is a surface-controlled process.Further studies showed that KY-2-22 strain could enrich and produce a large number of biofilms in the MFC anode,and could also form a white biofilm at the gas-liquid interface after liquid culture,when the bacterial liquid was statically placed at room temperature > 6 hours.The biofilm of KY-2-22 can be directly used for the assembly of microbial fuel cells after forming.Its power generation capacity is basically the same as that of the conventional MFC of KY-2-22,and its electrochemical behavior analysis shows the same process of surface control.—— Thus,it is more confirmed that KY-2-22 strain can perform surface-controlled electrochemical processes during power generation,and the particularity of treating KY-2-22 as a newly discovered power-producing strain is also highlighted.However,the electrochemical activity and electricity-producing activity of the biofilm formed by KY-2-22 strain at the gas-liquid interface are better than that of the anode biofilm produced by the bacterial strain Shiva's CN32 strain after discharge,which proves that the biofilm produced by KY-2-22 strain in particular has excellent performance at the gas-liquid interface.In the end of this thesis,conclusions are made briefly and perspectives of the future applications of the bacteria isolated from animals.Thus,it is proved that KY-2-22 is a new special electricity-producing bacterium,which can produce electricity by surface-controlled chemical behavior,and also can produce a large number of excellent performance biofilm under the condition of static room temperature.In the end of this thesis,conclusions are made briefly and perspectives of the future applications of the bacteria isolated from animals.