Escherichia coli inactivation by water-soluble, ozonated C60 derivative: kinetics and mechanisms

Antibacterial and bactericidal effects of a C60 derivative prepared via excess ozonation of C60 aggregates in water were investigated using Escherichia coli as a representative microorganism. Ozonated C60 up to 10 mg/L did not cause significant growth inhibition nor inactivation of E. coli in the absence of either oxygen or light. However, it readily inactivated E. coli in the presence of both oxygen and light at much faster rate than parent C60 aggregates, suggesting involvement of photochemical generation of reactive oxygen species (ROS). Among ROS, hydroxyl radical was found as a primary agent for the cell inactivation. Little surface protein release and concurrent intercellular enzyme degradation during the course of E. coli inactivation, along with visual evidence obtained from transmission electron microscopic analysis, collectively indicated that the mechanism of E. coli inactivation by ozonated C60 involves efficient penetration of ozonated C60 into E. coli and subsequent photochemical production of hydroxyl radical within the cell cytoplasm. These findings suggest that oxidative transformation of C60 can lead to increased toxicity in addition to increased water solubility and reduced size, warranting further studies on other potential chemical derivatization possible in natural and engineered environments for an accurate assessment of environmental impact of this class of materials.