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, warrantingfurtherstudiesonotherpotentialchemicalderivatization possible in natural and engineered environments for an accurate assessment of environmental impact of this class of materials.