Inactivation of antibiotic resistance genes by nanoscale zero-valent iron modified biochar composites: Synergistic effect of oxidative damage and physical destruction

Pollution of antibiotic resistance genes (ARGs) has become a challenge in the One Health era. Application of biochar-based materials is a strategy for controlling biological pollutants in water environment. However, the performance of nanoscale zero-valent iron (nZVI) modified biochar for inactivating antibiotic resistance bacteria (ARB) and extracellular ARGs (eARGs) in aquaculture environment is unknown. Therefore, a batch of nZVI modified softwood pellet derived biochar (SBC) composites (nZVI-SBCs) with different Fe: SBC mass ratio was synthesized to investigate their performance for inactivating E. coli HB101 and plasmid IE-V1955 as the correspondingly representative ARB and eARGs. The nZVI-SBCs with chain-like aggregates consisting of spherical nZVI dispersed on SBC surfaces contained high Fe0 content (28.2-33.3 %) and thin iron oxides layer. The nZVISBCs decreased E. coli HB101 number by 58.1-99.8 %, following an order of nZVI-SBC2 > nZVI-SBC1 > nZVISBC0.5. No regrowth of E. coli HB101 treated with nZVI-SBCs was observed. The inactivation of E. coli HB101 by nZVI-SBCs was attributed to the synergistic effect of cell membrane damages mediated by the extracellular ROS generation, intracellular ROS overproduction induced by Fe2+ overload, and bacterial coagulation by iron corrosion products. Moreover, nZVI-SBCs decreased the abundance of blaTEM-1 gene on plasmid IE-V1955 by 0.19-4.64 log, thus inhibiting their horizontal transformation. Inactivation of plasmid IE-V1955 was due to the strand breaks and base damages by the generated ROS from nZVI-SBCs. Density functional theory calculations results showed that center dot OH originated from nZVI-SBCs destroyed phosphodiester bond and hydrogen bond between G-C base pairs through dehydrogenation reaction. These findings expand the understanding of nZVI-SBCs inactivating ARG pollution, and also provide a practical strategy to mitigate ARG pollution in aquaculture environment based on biochar-based functional materials.