Goethite nanoparticles binding DNA in dissemination of antibiotic resistance genes: new insights into the role of inorganic phosphate with 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 (Pi_e), remains unclear. Using goethite (a representative FeO mineral) and diverse DNA forms (three linear fragments, one ARG-carrying plasmid), this study quantified Pi_e-driven DNA desorption via a novel successive desorption–extraction protocol, distinguishing readily desorbable DNA from residual DNA. Pi_e (1.0–10 mg P L⁻¹) displaced 5–96% of adsorbed DNA. Structurally, the shorter linear DNA and supercoiled plasmid formed fewer Fe–O–P bonds per adsorbed molecule, enhancing Pi_e-driven displacement and subsequently increasing their desorbable fraction, yielding a two-stage response to Pi_e fluctuations (minimal below 0.2–0.5 mg P L⁻¹; substantial above). Critically, Escherichia coli transformation assays showed that while goethite adsorption suppressed ARG transfer, Pi_e-activated desorption restored transformation efficiency. These results resolve the unverified link between realistic Pi_e 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.