Research On Mechanisms Of Extracellular Electron Transfer For Shewanella Strains Using Microbial Electrochemical Technologies

Microorganisms are living organisms and widespread in the world.Extracellular electron transfer(EET)in microorganisms has attracted many interests in recent years,because the process was found to be important to biogeochemical cycling,as well as iron corrosion,biosynthesis,and bioelectrochemical systems.Microbial electrochemical technology is one of efficient methods for studying the mechanism of microbial extracellular electron transfer.The core difference with other energy conversion systems(such as fuel cells)is that microorganisms exist on the interface of electrode/solution,and the energy and matter conversion are realized by their respiratory and metabolism.To improve the ability of microbial extracellular electron transport and improve the efficiency of conversion,it is important to study the extracellular electron transfer mechanism at the electrode/solution interface by physical chemistry.In this thesis,electrochemistry and its combined techniques are used to study the mechanisms of extracellular electron transfer for Shewanella,which is one of electrochemically active microorganisms.The main contents are as follows:1.The electrochemical redox properties of Shewanella oneidensis MR-1 and Shewanella woodyi were studied by electrochemical techniques,including cyclic voltammetry,differential pulse voltammetry.According to voltammograms,S.woodyi has similar redox properties with S.oneidensis MR-1,and S.woodyi has the ability to transfer electron from cells to the electrode.In order to form biofilm on the electrode,an ITO was set as electron acceptor by controlling the applied potential.The morphology of cell and biofilms were characterized by electron microscopy,the results showed that the morphology was changed from rod-like to network before and after biofilm formation.Besides,when changing the potential scanning rate in cyclic voltammetry,the anodic and cathodic peak currents have linear relation with scan rate or the scan rate square root.The electron transfer pathways which may be proposed according to the electrode reaction kinetics.Based on all electrochemical properties,it can be concluded that electron transfer from cell to cell may be one of extracellular electron transfer pathways for Shewanella.2.Redox mediators interact with bacterial cells and they are used in fundamental study of cell redox activities.To understand the interactions of microbes with these mediator molecules,it is necessary to perform rapid,real-time spatial identification of biofilm.In this study,ferrocenemethanol,a small redox mediator and soluble ferrous salt,was introduced to investigate the electrode process by using cyclic voltammetry techniques.The results revealed that the electrode process was in accordance with a mechanism of electrochemical following microbial catalysis.Furthermore,the spatial identification of S.oneidensis MR-1 was achieved on the penetration mode and the feedback mode by using scanning electrochemical microscopy.Therefore,the SECM analysis using specific redox mediator is a useful tool in detecting electrode process of microbial cells.The application of bringing SECM into microbial electrode reactions with redox mediators will offer a simple,rapid and label-free monitoring method.3.To investigate the relationships between bioluminescence and EET,an electro-chemiluminescence apparatus incorporating a three-electrode cell integrated with a luminescence detector was set up to simultaneously record electrochemical data and luminescence signals.We tested the electrochemical activity of the luminous S.woodyi using electrochemical technologies and in vivo imaging systems.Moreover,electro-chemiluminescence revealed an interaction between bioluminescence and extracellular electron transfer,when the direction of the sweep potential was different in charge and discharge states,respectively.S.woodyi was shown to be a useful model organism for studying both oxidation and reduction reactions at the interface of microbes and solid substrates,and a possible electron transfer pathway was proposed.