Thioredoxin-mediated sulfur cycling and biogenic sulfur encapsulation synergistically enhance co-removal of nitrogen, sulfamethoxazole, and resistance genes in constructed wetlands.

The interplay between sulfur-driven denitrification and antibiotic resistance genes (ARGs) proliferation remains unresolved in constructed wetlands (CWs), where sulfide accumulation and reactive oxygen species generation paradoxically enhance nitrogen removal while compromising microbial integrity. To resolve this conflict, this study engineered a FeS@S° composite filler that synergized thioredoxin (Trx)-mediated sulfur cycling and biogenic sulfur (bio-S) encapsulation. Upregulation of trxA/B genes (2.3-fold increase) enabled Trx to convert toxic sulfide into adhesive bio-S, exhibiting higher microbial adhesion that shielded functional denitrifiers like Thiomonas (84.03 % viability under SMX stress). Concurrently, sulfur vacancies (SVs) at FeS {210} crystal facets generated hydroxyl radicals (•OH) and singlet oxygen (¹O₂) via vacancy-activated pathways, selectively degrading about 73.00 % of extracellular polymeric substance (EPS)-bound ARGs while suppressing horizontal gene transfer (tolC downregulation). The 6:4 FeS@S system achieved 68.66 % total nitrogen removal and 50.17 % sulfamethoxazole degradation, outperforming conventional substrates by 28.00-39.00 %, alongside a 61.24-67.31 % reduction in ARG abundance. A self-sustaining sulfur cycle recycled about 89.00 % of sulfides into bio-S or FeS, minimizing HS emissions (0.045 mg·m·h) and maintaining electron flux. By bridging Trx-driven redox homeostasis and bio-S's physical protection, this work redefines CWs as robust systems capable of simultaneous nitrogen retention, antibiotic degradation, and ARGs suppression, establishing a transformative paradigm for sustainable wastewater treatment.