Response of the microbial community structure of biofilms to ferric iron in microbial fuel cells.

Ferric iron can affect the current generation of microbial electrochemical system (MES); however, how it influences microbial biofilm formation and metabolic activity has not been reported. Here, we describe the response of microbial electrode biofilm communities to insoluble ferric iron (Fe3+ ) at different concentrations in microbial fuel cells (MFCs). Insoluble ferric iron (200μM) improved electrochemical activity of the MFCs microbial biofilms during start-up and resulted in a higher maximum power density of 0.95W/m2 , compared with the control (0.76W/m2 ), 500μM Fe3+ (0.83W/m2 ), 1000μM Fe3+ (0.73W/m2 ), and 2000μM Fe3+ (0.59W/m2 ) treatments. Illumina Hiseq sequencing of 16S rRNA gene amplicons indicated that the predominant populations in the anode biofilms of the MFCs belonged to Geobacter, with relative abundance of 66-75%. Microbial cathode biofilm communities were more susceptible to Fe3+ , as an obvious shift in the cathode biofilm community structures occurred as Fe3+ concentration was increased. The most predominant populations in the MFC cathode biofilms without Fe3+ and with 200μM Fe3+ were affiliated with Thauera (46% and 35%), whereas no absolutely predominant populations were present in the MFC cathode biofilm with 1000μM Fe3+ . The results demonstrate that a low concentration of Fe3+ facilitated the power output of MFCs and shaped community structures of the electrode biofilm.