Self-sustaining Fe-S redox cycling by Aromatoleum evansii LY15 enables robust denitrification and atrazine degradation.

Abstract

Agricultural wastewater typically contains nitrate (NO₃^--N) and atrazine (ATZ), while autotrophic denitrification driven by pyrite is hindered by surface passivation. This study reported the isolation of Aromatoleum evansii LY15 and demonstrated a self-sustaining iron-sulfur (Fe-S) redox cycle that alleviated passivation and maintained electron flux for robust NO₃^--N removal. Batch assays using soluble Fe²⁺/Fe³⁺, thiosulfate, sulfate, and natural pyrite revealed that the combination of Fe²⁺ and thiosulfate achieved the highest NO₃^--N removal efficiency (80.86 %) among all tested soluble electron donors. Pyrite (4 g L^-1, 80 mesh) facilitated near-complete NO₃^--N removal (99.95 %) within 144 h and effectively promoted the removal of total phosphorus from real wastewater samples under neutral pH. Dialysis experiments found that direct cell-mineral contact was essential for efficient electron exchange. Electrochemical analyses revealed a sharp decrease in charge-transfer resistance and intensified Fe-S redox currents, confirming microbially mediated pyrite activation. The presence of secondary Fe-S phases (e.g., Fe₃O₄, FeS, Fe₃S₄) and intermediate sulfur species (S⁰/S_n^2-) signals verified dynamic Fe-S cycling. ATZ exhibited concentration-dependent effects, with concentrations of 0.5-1.0 μM stimulating denitrification, extracellular electron transfer, and Fe-S cycle. Electron paramagnetic resonance and mass spectrometry analyses revealed free radical pathways (SO₃^·-, ·OH) and biological transformations as the primary mechanisms accounting for more than 95 % ATZ removal at low concentrations. Overall, strain LY15 orchestrated a bidirectional Fe-S cycle that alleviated pyrite passivation, coupling NO₃^--N removal with ATZ attenuation, establishing a practical paradigm for resilient mineral-based treatment of complex agricultural wastewater.