Coupling electron snorkels with biogenic FeS_x-associated interfacial structures enhances anaerobic petroleum...

Petroleum hydrocarbon (PHC) degradation in oxygen-limited soils is constrained by scarce terminal electron acceptors and poor redox connectivity. Coupling Fe and S transformations with conductive electron snorkels is expected to stimulate anaerobic PHC turnover by promoting Fe/S redox cycling and syntrophic electron exchange, yet the underlying mechanism remains unclear. Here, a dual electron-transfer framework was developed by integrating in situ biogenic FeS_x-associated assemblages with electron snorkels. In systems amended with exogenous γ-FeOOH + snorkel + S⁰ or Fe-rich natural soil + snorkel + S⁰ (HFe-SN+S), PHC removal increased by ∼2.4-4.1-fold relative to corresponding controls, and comparable enhancements were reproduced in an independent agricultural soil. These gains were accompanied by higher bulk ionic conductivity, transient Fe²⁺ accumulation, and FeS_x-enriched aggregate coatings, indicating enhanced ion release and Fe/S redox turnover. HFe-SN + S reshaped Fe/S cycling and enriched Fe-S-transforming and PHC-degrading consortia carrying genes for PHC catabolism and extracellular electron transfer. Redox-coupled N transformation provided an auxiliary electron sink, mitigating electron accumulation and coinciding with faster TOC depletion and IC production. Overall, these findings support a mechanistic framework in which FeS_x-associated interfacial structures may facilitate local electron exchange, while snorkels provide a potential electron-disposal route, establishing a theoretical basis for Fe-S-snorkel-assisted remediation strategies.