On the cause of the tailing phenomenon during virus disinfection by chlorine dioxide

This study investigates the mechanisms underlying the deviation from Chick-Watson kinetics, namely a tailing curve, during the disinfection of viruses by chlorine dioxide (ClO2). Tailing has been previously reported, but is typically attributed to the decay in disinfectant concentration. Herein, it is shown that tailing occurs even at constant ClO2 concentrations. Four working hypothesis to explain the cause of tailing were tested, namely changes in the solution’s disinfecting capacity, aggregation of viruses, resistant virus subpopulations, and changes in the virus properties over the course of reaction. In experiments using MS2 as a model virus, it was possible to rule out the solution’s disinfecting capacity, virus aggregation and the resistant subpopulation as reasons for tailing. Instead, the cause for tailing is the deposition of an adduct onto the virus capsid over the course of the experiment, which protects the viruses. This adduct could easily be removed by washing, which restored the susceptibility of the viruses to ClO2. This finding highlights an important shortcoming of ClO2, namely its self-limiting effect on virus disinfection. It is important to take this effect into account in treatment applications to ensure that the water is sufficiently disinfected before human consumption

Virus inactivation mechanisms: impact of disinfectants on virus function and structural integrity

Oxidative processes are often harnessed as tools for pathogen disinfection. Although the pathways responsible for bacterial inactivation with various biocides are fairly well understood, virus inactivation mechanisms are often contradictory or equivocal. In this study, we provide a quantitative analysis of the total damage incurred by a model virus (bacteriophage MS2) upon inactivation induced by five common virucidal agents (heat, UV, hypochlorous acid, singlet oxygen, and chlorine dioxide). Each treatment targets one or more virus functions to achieve inactivation: UV, singlet oxygen, and hypochlorous acid treatments generally render the genome nonreplicable, whereas chlorine dioxide and heat inhibit host-cell recognition/binding. Using a combination of quantitative analytical tools, we identified unique patterns of molecular level modifications in the virus proteins or genome that lead to the inhibition of these functions and eventually inactivation. UV and chlorine treatments, for example, cause site-specific capsid protein backbone cleavage that inhibits viral genome injection into the host cell. Combined, these results will aid in developing better methods for combating waterborne and foodborne viral pathogens and further our understanding of the adaptive changes viruses undergo in response to natural and anthropogenic stressors

Inactivation of bacteriophage MS2 with potassium ferrate(VI)

Abstract - Ferrate [Fe(VI); FeO42-] is an emerging oxidizing agent capable of controlling chemical and microbial water contaminants. Here, inactivation of MS2 coliphage by Fe(VI) was examined. The inactivation kinetics observed in individual batch experiments was well described by a Chick-Watson model with first-order dependences on disinfectant and infective phage concentrations. The inactivation rate constant ki at a Fe(VI) dose of 1.23 mgFe/L (pH 7.0, 25oC) was 2.27(±0.05) L/(mgFe×min), corresponding to 99.99% inactivation at a Ct of ~4 (mgFe×min)/L. Measured ki values were found to increase with increasing applied Fe(VI) dose (0.56-2.24 mgFe/L), increasing temperature (5-30C), and decreasing pH conditions (pH 6-11). The Fe(VI) dose effect suggested that an unidentified Fe by-product also contributed to inactivation. Temperature dependence was characterized by an activation energy of 39(±6) kJ mol-1, and ki increased >50-fold when pH decreased from 11 to 6. The pH effect was quantitatively described by parallel reactions with HFeO4- and FeO42-. Mass spectrometry and qRT-PCR analyses demonstrated that both capsid protein and genome damage that increased with the extent of inactivation, suggesting that both may contribute to phage inactivation. Capsid protein damage, localized in the two regions containing oxidant-sensitive cysteine residues, and protein cleavage in one of the two regions may facilitate genome damage by increasing Fe(VI) access to the interior of the virio