Microbial Community Structure Of Microbial Fuel Cells In Paddy Soil And Its Different Response To Substrate

Plant microbial fuel cell (PMFC) is a new fuel cell technology that can generate electricity by utilizing solar energy through plant/microbe cooperation. It shows a rapid progress due to efforts of several world-leading laboratories in recent years. PMFC can transfer renewable solar energy to electric energy in a green, efficient and sustainable way thus has unique advantages over traditional and common energy resources. The extracellular electron transfers (EET) in paddy soil have been documented by a series of studies on microbial fuel cells (MFCs). Microbial community involved in electron transfers in paddy soil MFC, however, remains poorly understood. In the present experiment, I constructed paddy soil MFCs to determine the bacterial and archaeal communities in the anode-associated soil.The preliminary research showed that the electrical current in closed circuit MFCs increased rapidly with the plant growth. By comparison, MFCs without rice plant produced minor current. Methane emission decreased relatively in closed circuit MFCs compared with open circuit MFCs that did not generate electricity output. Analyses with multiple molecular methods including454pyrosequencing revealed that the upstream fermentation bacterial community was not significantly affected by MFC operation. However, the relative abundances of Geobacteraceae increased markedly in MFCs planted with rice. Furthermore, the syntrophs including Syntrophaceae, Syntrophorhabdaceae, Syntrophobacteraceae and Syntrophomonadaceae increased. Notably, Geobacteraceae and these syntrophs also increased, albeit to a lesser extent, in the open circuit MFCs compared with no-plant control. Among methanogenic archaea, the relative abundance of Methanosaetaceae increased significantly in closed circuit MFCs compared with open-circuit MFCs. Thus, this study suggests that not only electrogenesis active bacteria Geobacteraceae but also syntrophs was enhanced in the planted MFCs and Methanosaetaceae were promoted among methanogens.Further investigation found that the current flow can be promoted over30%by adding rice straw into PMFCs. However, the straw did not influence the treatments without rice plant. Rice straw as a kind of external substrate had multiple effect on microbes in paddy soil while the presence of plant is necessary for high efficiency electricity generation. Besides, electrogenesis had remarkable fluctuation along with the diurnal variation and the current output of MFCs with rice plant decreased largely at night compared with no-plant control.In all, this research had a preliminary study on paddy soil MFC and demonstrated that the presence and growth of plant can promote electrogenesis. Also, methanogenesis could be suppressed to a certain extent. The microbial community structure of anode-associated paddy soil as well as the effect of diurnal cycle and external substrates were also analysed. This research laid a foundation at this newly rising area for next step studies.