Mechanisms of action of chlorella biochar-loaded nano zero-valent iron systems on Escherichia coli: Insights from cell biology and untargeted metabolomics

Surface modification can significantly improve nano zero-valent iron (nZVI) stability. However, different methods and materials significantly affect nZVI toxicity, and the effects on bacterial metabolic processes and corresponding molecular mechanisms require further study. In this study, Chlorella biochar-loaded nano zero-valent iron (nZVI/BC) was prepared, showing optimum removal of Microcystis aeruginosa ( M. aeruginosa ) at a dosing rate of 12.5 g L −1 . The toxicity against Escherichia coli ( E. coli ) was investigated, revealing time-dependent inactivation efficiency, achieving −3.60 log at 30 min and −5.0 log for a single nZVI. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) analyses revealed that nZVI exhibited stronger adsorption to cells compared to nZVI/BC, with both nZVI and nZVI/BC primarily interacting with amine, carboxyl, and ester groups on the cell surface. Physiological, biochemical, ROS quenching, and metabolomics experiments indicated that ROS played a key role in the inactivation of E. coli . This study proposes a strategy to balance the stability of nZVI with its biocompatibility. • nZVI/BC contact is crucial for E. coli colonization, stress response, and virulence. • Amino acid, nucleotide, and lipid metabolism in E. coli are significantly disrupted. • The loading role of BC is crucial for reducing the toxicity of nZVI. • Functional groups of E. coli cell membranes are severely disrupted.