Effects of anode potential acclimation on sulfate-reducing bacteria-driven microbial fuel cell performance: Community structure, functional gene shifts, and a putative metabolic model.

This study investigated the electrochemical, microbial, and metagenomic characteristics of microbial fuel cells (MFCs) operated at different poised anode potentials (-0.4 V, 0 V, and + 0.4 V vs. Standard Hydrogen Electrode), inoculated with the sulfate-reducing bacteria (SRB)-enriched consortium from real shale gas fracturing flowback water. Marked performance differences were observed across the individually operated reactors after acclimation, with the reactor poised at -0.4 V showing the highest sulfate removal efficiency (75%) and power density (0.63 W/m2). Electrochemical analyses indicated the highest electrochemical activity in the -0.4 V anode biofilm. Metagenomic analysis revealed that Nitratidesulfovibrio vulgaris (N. vulgaris) was substantially more abundant in the -0.4 V reactor (16%) than in the other reactors, where it was the dominant SRB taxon. Functional gene profiling of the dissimilatory sulfate reduction (DSR) and extracellular electron transfer (EET) systems showed that N. vulgaris was the taxon to which DSR genes and the pilin subunit genes flp and pilA were predominantly assigned based on best-hit annotation, suggesting a possible direct EET route via a pilus system. Furthermore, the fermentative genus Trichococcus also showed higher relative abundance in this reactor, and nfrA1 was predominantly assigned to this taxon (best-hit annotation), pointing to a potential role in flavin-mediated indirect EET. Collectively, these observations indicate that the -0.4 V reactor was associated with a distinct community structure and functional gene abundance profile, providing a putative metabolic model that may guide future exploration of SRB-MFCs targeting sulfate-rich wastewater.