The S.Oneidensis MR-1 Extracellular Electron Transfer Pathway In The Process Of Co-Culture

S.oneidensis MR-1 is one of an important model electricity producing bacteria with the function of extracellular electron transfer, which allows the electron producing by respiratory chain transmit to the solid-state electron acceptor such as iron. Thus this bacteria has been widely used in the microbial fuel cell system. A lot of research work have been proceeded on the electron metabolic pathway of S.oneidensis MR-1. Two major metabolic pathways have been proposed: one is for iron oxide metabolism and the other is for iron sulfide metabolism. For iron oxide pathway, electrons are transferred from Cym A to the metal restore protein Mtr A by fumarate reductase FccA or transferred directly to Mtr A, and the electron transfer from the cytoplasm to the cell membrane surface through the liposome membrane by a series of metal restore protein MtrA, B, C. For iron sulfide pathway, the electrons are delivered into the cytoplasm and transferred to the outer surface of the cell by PsrA, PsrB, psrC proteins. When the electrons are transferred to the outer surface of the cell, the electrons will be further transferred to the extracellular electron acceptors mediated by cytochrome C, microbial nanowires and other mechanisms.Co-culture of bacteria often produce more electrical power than pure culture in microbial fuel cells under certain condition. Therefore, researchers start to pay more attention to mechanism of electricity production in the process of co-culture. However, the metabolic pathway of Shewanella MR-1 in co-culture has not been studied in detail. In this paper, we studied expression of key genes related with electric metabolic pathway and the basic electrochemical character of S.oneidensis MR-1 of co-culture in a double chamber microbial fuel cell (MFC) system. Meanwhile, we analyzed the population dynamics of microbial community contained S.oneidensis MR-1 by using 16sRNA gene sequencing and other analytical tools to discuss the change of the electrochemical characteristics of MFC under different culture conditions and study the variation of the electron metabolic pathway under the condition of double co-culture and co-culture of S.oneidensis MR-1 with iron reducing microbial community.We observe and record the data of each MFC device through at least three cycles; plot the polarization curves, cyclic voltammetry curves, open circuit voltage OCV curves, power density curves of MFC devices under different culture condition and discuss the data of inter resistance, capacitance, open circuit voltage, power density,maximum theoretical power generation efficiency, coulomb efficiency. The data proves that mixed bacterial culture is inclined to produce more electrical power and improve the electro-chemical performance of MFC devices. At the same time, the mixed bacterial culture also help to reduce the internal resistance and improve the coulomb efficiency of MFC devices.With increase of culture time, the expression of MtrA? MttB?MtrC?OmcA genes have increased on the anode electrode of S.oneidensis MR-1 MFC devices to some extent. It proves that these genes are related to the electron metabolic pathway of S.oneidensis MR-1; the relative expression of OmcA gene has been significantly improved, which proves that double co-culture play a role in the process of electron transferring from the extracellular to the electron acceptor. After we put ferric citrate into the MFC devices with co-culture of Shewanella MR-1 and the other co-culture, the relative expression of MtrA, MtrB, mtrC genes have significantly improved. On one hand,it shows the iron oxide and MtrA, MtrB, mtrC gene expressions are closely related with each other. On the other hand, it shows that the electron metabolic pathway of S.oneidensis MR-1 has changed under this culture condition. These changes play a positive role in the electron transfer in S.oneidensis MR-1 MFC system, which influence the electron transfer in the mix culture.