Dynamic aqueous transformations of lithium cobalt oxide nanoparticle induce distinct oxidative stress responses ofB. subtilis

Lithium cobalt oxide (LiCoO₂), an example of nanoscale transition metal oxide and a widely commercialized cathode material in lithium ion batteries, has been shown to induce oxidative stress and generate intracellular reactive oxygen species (ROS) in model organisms. In this study, we aimed to understand the time-dependent roles of abiotic ROS generation and Co ions released in aqueous medium by LiCoO₂NPs, and examined the induced biological responses in model bacterium,B. subtilisupon exposure. We found that the redox-active LiCoO₂NPs produced abiotic ROS primarily through H₂O₂generation when freshly suspended. Subsequently, the freshly-suspended LiCoO₂NPs induced additional DNA breakage, and changes in expression of oxidative stress genes inB. subtilisthat could not be accounted for by the released Co ions alone. Notably, in 48 hour old LiCoO₂suspensions, H₂O₂generation subsided while higher concentrations of Co ions were released. The biological responses in DNA damage and gene expression to the aged LiCoO₂NPs recapitulated those induced by the released Co ions. Our results demonstrated oxidative stress mechanisms for bacteria exposed to LiCoO₂NPs were mediated by the generation of distinct biotic and abiotic ROS species, which depended on the aqueous transformation state of the NPs. This study revealed the interdependent and dynamic nature of NP transformation and their biological consequences where the state of NPs resulted in distinct NP-specific mechanisms of oxidative injury. Our work highlights the need to capture the dynamic transformation of NPs that may activate the multiple routes of oxidative stress responses in cells.