Environmental electron shuttle impacting nano-bio interactions via bio-activity-dependent mechanism

Numerous studies have demonstrated that the outcomes of nano-bio interactions are influenced by a complex interplay of nanoparticles (NPs), test organisms, and environmental molecules together. Recently, the formation of an eco-corona through the adsorption of environmental molecules onto NP surfaces and its impact on nano-bio interactions has become a central focus in nanotoxicology research. However, some environmental molecules can also modulate the outcomes of nano-bio interactions independently of corona formation. In this study, Escherichia coli (E. coli) were exposed to ceria (CeO₂) NPs at concentrations of 10, 20, and 50 mg/L, both in the presence and absence of 0.1 mM menadione (MD). Our findings indicate that the presence of MD significantly increased the dissolution of ceria NPs on the bacterial surface. This enhancement is likely due to MD's role as an electron shuttle, facilitating electron transfer between the inner and outer bacterial membranes and promoting the reduction of ceria NPs. The reduced ceria NPs subsequently released Ce³⁺ ions, leading to severe heavy metal toxicity as evidenced by increased ATP consumption and oxidative stress. Consequently, MD exacerbated the dose-dependent toxicity of ceria NPs against E. coli, despite MD exposure alone having minimal effect on bacterial viability. These results confirm that environmental molecules can profoundly impact the outcomes of nano-bio interactions by altering the cellular activities and functions of the test organisms. This study provides valuable insights that will deepen our understanding of the complex dynamics of nano-bio interactions within environmental matrices and advance our knowledge of nanotoxicological mechanisms.