Mechanistic insights into Fe2O3-mediated directional electron transfer driving anaerobic microbial interactions for enhanced 4-chlorophenol degradation.

Anaerobic degradation of recalcitrant pollutants remains a significant challenge due to insufficient electron supply. Interspecies electron transfer (IET) based on extracellular electron transfer (EET) processes plays a crucial role in supporting the cooperative metabolism of complex microbial consortia. Here, an Fe2O3-coupled anaerobic system driven by a potential gradient was constructed to enhance the degradation of 4-chlorophenol (4-CP), achieving a removal efficiency 1.38 times that of conventional anaerobic treatment. Fe(II)/Fe(III) redox cycling coupled with cytochrome c-mediated EET overcame the limitation of short-range electron transfer between outer-membrane electroactive proteins and conductive materials, thereby activating direct IET among methanogens, fermentative bacteria, degraders, and iron-reducing bacteria. Fe2O3 not only reshaped the microbial community but also enhanced pyruvate metabolism and gluconeogenesis, promoted heme biosynthesis and cytochrome c assembly, and strengthened cytochrome c-mediated electron transport for extracellular electron uptake, while reducing dependence on NADH dehydrogenase. The stimulated interspecies cooperation facilitated multiple 4-CP degradation routes, including dechlorination, hydrolysis, and substitution. Molecular dynamics simulations (MDS) further verified efficient electron exchange between Fe2O3 and the heme, which contributes to the establishment of a long-range microbial electron transfer network. Fe2O3-mediated directional electron transfer restructured microbial energy metabolism and interspecies interactions, providing a robust strategy for the anaerobic remediation of chlorophenol-contaminated wastewater.