Mechanisms underlying the role of Fe3O4 in enhancing antibiotic degradation and mitigating the spread of antibiotic resistance in aquaculture sediment: Coupling dissimilatory iron reduction with methanogenesis.

Ferric oxides play a critical role in transforming organic contaminants within anaerobic aquaculture sediments; however, their effect on the removal of antibiotics and antibiotic resistance genes (ARGs) remains unexplored. This study revealed that the addition of Fe3O4 significantly promoted microbial Fe(III) reduction, SMX degradation, and methanogenesis by enhancing metabolic activity and facilitating electron transfer. While nutrient supplementation similarly improved SMX removal, it notably increased ARG abundance, unlike Fe3O4, which effectively suppressed ARGs. Although the presence of the electron shuttle AQDS in Fe3O4-amended systems further stimulated dissimilatory iron reduction, no additional benefit to SMX degradation was observed. Inhibition of methanogenesis reduced SMX degradation by 48 %, whereas Fe3O4 supplementation enriched the methane metabolic pathway, suggesting that SMX removal occurred through a conductive network involving Fe3O4 and methanogens. Moreover, Fe3O4 supplementation induced significant shifts in bacterial community composition, enhanced antioxidase activity, and reduced reactive oxygen species levels. These alterations were associated with the repression of genes related to horizontal gene transfer and a decrease in ARG hosts. Overall, these results indicate that Fe3O4 serves as an effective conductor, enhancing antibiotic degradation and limiting ARG propagation in aquaculture sediments.