Insight into the primary mode of action of TiO2 nanoparticles on Escherichia coli in the dark

Large‐scale production and incorporation of titanium dioxide nanoparticles (NP‐TiO2) in consumer products leads to their potential release into the environment and raises the question of their toxicity. The bactericidal mechanism of NP‐TiO2 under UV light is known to involve oxidative stress due to the generation of reactive oxygen species. In the dark, several studies revealed that NP‐TiO2 can exert toxicological effects. However, the mode of action of these nanoparticles is still controversial. In the present study, we used a combination of fluorescent probes to show that NP‐TiO2 causes Escherichia coli membrane depolarization and loss of integrity, leading to higher cell permeability. Using both transcriptomic and proteomic global approaches we showed that this phenomenon translates into a cellular response to osmotic stress, metabolism of cell envelope components and uptake/metabolism of endogenous and exogenous compounds. This primary mechanism of bacterial NP‐TiO2 toxicity is supported by the observed massive cell leakage of K+/Mg2+ concomitant with the entrance of extracellular Na+, and by the depletion of intracellular ATP level.