Iron modulation of sulfur-mediated autotrophic denitrification: denitrification efficiency, microbial succession, and metabolic pathways

The application of iron sulfide-mediated autotrophic denitrification is promising for nitrate reduction in carbon-deficient wastewater and polluted groundwater. Previous studies have shown distinct functional microbial communities in different iron sulfide-mediated autotrophic denitrification systems, obscuring how iron modulates their composition and activity. In this study, iron-modulated sulfur autotrophic denitrification efficiency, microbial succession, and key pathways were investigated at different iron levels. Results showed that 1 mM Fe²⁺ enhanced denitrification efficiency (91.1 %) and prevented cell encrustation. Metagenomic analysis indicated that phylum Campylobacterota (16.0 %) and genus Sulfurimonas (14.4 %) were enriched under iron-modulated conditions. Iron modulated nitrate reduction by improving the relative abundance of complete denitrification genes (napA, napB, and nosZ) and stimulating sulfur metabolism through the SOX complex pathway (soxZ and soxY). These findings reveal the role of iron in modulating sulfur-mediated autotrophic denitrification and provide new insights into the microbial mechanisms involved in iron-sulfur coupling systems.