Unusual microbial community and impact of iron and sulfate on microbial fuel cell ecology and performance

The present energy and the waste accumulation crisis make the development of bioelectrochemical systems each day more important as a technology for coupled waste-treatment, electricity production, and biorefinement, whilst closing the circular economy loop. However, its application is still hampered by the complexity of its biocatalysts. This study evaluated, from an ecological and metabolic point of view, Microbial Fuel Cells (MFCs) inoculated with Brazilian marine sediment and fed with synthetic wastewaters contaminated with iron and sulfate, containing acetate as carbon source. Making use of 16S rRNA gene amplification analyses and physical- and electrochemical assays, a stable core community was observed throughout different treatments, lacking in the taxa traditionally affiliated with MFCs, while rich in alkaliphiles and acetogens, namely Desulfomicrobium, Advenella, Tindallia, Clostridium, and Desulfuromonas. MFCs supplemented with iron and sulfate obtained more stable electrochemical performances, although the core microbial community remains unchanged, apart from a slight shift within the relative dominance of each group within the core. The use of these common pollutants affected the nutritional profile by activating different metabolic pathways for iron and sulfate cycling coupled to the ubiquitous nutrients, while strongly influencing ammonia balance. This study highlights the hidden potential to be explored in novel inocula from this still poorly investigated Southern Hemisphere and provides insights into what may be used as tools to better manipulate the communities constituting MFC bioanodes.