Goethite nanoparticles binding DNA in dissemination of antibiotic resistance genes: New insights into the role of inorganic phosphate under environmentally relevant concentrations

Abstract

Iron (oxyhydr)oxides (FeO) significantly influence the environmental dissemination of antibiotic resistance genes (ARGs) by adsorbing ARG-carrying DNA through phosphate interactions. However, the fate of FeO-adsorbed DNA, particularly its release dynamics and impact on ARG dissemination in the presence of inorganic phosphate with environmentally relevant concentrations (Pie), remains unclear. Using goethite (a representative FeO mineral) and diverse DNA forms (three linear fragments, one ARG-carrying plasmid), this study quantified Pie-driven DNA desorption via a novel successive desorption-extraction protocol, distinguishing readily desorbable from residual DNA. Pie (1.0–10 mg-P/L) displaced 5%–96% of adsorbed DNA. Structurally, shorter linear DNA and supercoiled plasmid formed fewer Fe-O-P bonds per adsorbed molecule, enhancing Pie-driven displacement and subsequently increasing their desorbable fraction, yielding a two-stage response to Pie fluctuations (minimal below 0.2–0.5 mg P/L; substantial above). Critically, Escherichia coli transformation assays showed that while goethite adsorption suppressed ARG transfer, Pie-activated desorption restored transformation efficiency. These results resolve the unverified link between realistic Pie fluctuations (e.g., paddy field fertilization/sediment hydrology) and FeO-bound DNA release, demonstrating its potential role in ARG dissemination. This mechanistic insight is essential for risk assessment of ARG transmission in iron-rich ecosystems and strategic deployment of FeO materials for soil ARG mitigation.