Mechanism of Ozone Inactivation of Bacteriophage f2

The inactivation kinetics of bacteriophage f2 were studied by using ozone under controlled laboratory conditions. The phage were rapidly inactivated during the first 5 s of the reaction by 5 and 7 logs at ozone concentrations of 0.09 and 0.8 mg/liter, respectively. During the next 10 min, the phage were further inactivated at a slower rate in both treatments. The [H]uridine-labeled f2 phage and its ribonucleic acid (RNA) were examined to elucidate the mechanism of ozone inactivation, utilizing adsorption to host bacteria, sucrose density gradient analysis, and electron microscopy. The specific adsorption of the phage was reduced by ozonation in the same pattern as plaque-forming unit reduction. RNA was released from the phage particles during ozonation, although it had reduced infectivity for spheroplasts. Electron microscopic examination showed that the phage coat was broken by ozonation into many protein subunit pieces and that the specific adsorption of the phage to host pili was inversely related to the extent of phage breakage. The RNA enclosed in the phage coat was inactivated less by ozonation than were whole phage, but inactivated more than naked RNA. These findings suggest that ozone breaks the protein capsid into subunits, liberating RNA and disrupting adsorption to the host pili, and that the RNA may be secondarily sheared by a reduction with and/or without the coat protein molecules, which have been modified by ozonation.