Bacterial Competition for the Anode Colonization under Different External Resistances in Microbial Fuel Cells

This study investigated the effect of external resistance (R-ext) on the dynamic evolution of microbial communities in anodic biofilms of single-chamber microbial fuel cells fueled with acetate and inoculated with municipal wastewater. Anodic biofilms developed under different R-ext (0, 330 and 1000 ohms, and open circuit condition) were characterized as a function of time during two weeks of growth using 16S rRNA gene sequencing, cyclic voltammetry (CV) and fluorescence microscopy. The results showed a drastic difference in power output of MFCs operated with an open circuit and those operated with R-ext from 0 to 1000 ohms. Two steps during the bacterial community development of the anodic biofilms were identified. During the first four days, nonspecific electroactive bacteria (non-specific EAB), dominated by Pseudomonas, Acinetobacter, and Comamonas, grew fast whatever the value of R-ext. During the second step, specific EAB, dominated by Geobacter and Desulfuromonas, took over and increased over time, except in open circuit MFCs. The relative abundance of specific EAB decreased with increasing R-ext. In addition, the richness and diversity of the microbial community in the anodic biofilms decreased with decreasing R-ext. These results help one to understand the bacterial competition during biofilm formation and suggest that an inhibition of the attachment of non-specific electroactive bacteria to the anode surface during the first step of biofilm formation should improve electricity production.