Correlation of Conformational Changes and Protein Degradation with Loss of Lysozyme Activity Due to Chlorine Dioxide Treatment

Bacterial inactivation processes in water disinfection - mechanistic aspects of primary and secondary oxidants - A critical review

Water disinfection during drinking water production is one of the most important processes to ensure safe drinking water, which is gaining even more importance due to the increasing impact of climate change. With specific reaction partners, chemical oxidants can form secondary oxidants, which can cause additional damage to bacteria. Cases in point are chlorine dioxide which forms free available chlorine (e.g., in the reaction with phenol) and ozone which can form hydroxyl radicals (e.g., during the reaction with natural organic matter). The present work reviews the complex interplay of all these reactive species which can occur in disinfection processes and their potential to affect disinfection processes. A quantitative overview of their disinfection strength based on inactivation kinetics and typical exposures is provided. By unifying the current data for different oxidants it was observable that cultivated wild strains (e.g., from wastewater treatment plants) are in general more resistant towards chemical oxidants compared to lab-cultivated strains from the same bacterium. Furthermore, it could be shown that for selective strains chlorine dioxide is the strongest disinfectant (highest maximum inactivation), however as a broadband disinfectant ozone showed the highest strength (highest average inactivation). Details in inactivation mechanisms regarding possible target structures and reaction mechanisms are provided. Thereby the formation of secondary oxidants and their role in inactivation of pathogens is decently discussed. Eventually, possible defense responses of bacteria and additional effects which can occur in vivo are discussed.

Laser Tweezers Raman Spectroscopy (LTRS) to Detect Effects of Chlorine Dioxide on Individual Nosema bombycis Spores

The microsporidium Nosema bombycis (Nb) causes pebrine, a fatal disease in sericulture. Nb is effectively killed by chlorine dioxide (ClO₂); however, the precise killing mechanism remains unclear. We used laser tweezers Raman spectroscopy (LTRS) to monitor the action of ClO₂ on individual Nb spores in real time. Raman peaks of ClO₂ appeared in Nb spores, corresponding to decreased peaks of trehalose that gradually disappeared. A peak (1658 cm^-1) corresponding to the protein α-helix significantly weakened while that (1668 cm^-1) corresponding to irregular protein structures was enhanced; their intensities were negatively correlated in a certain time range and dependent on ClO₂ concentration. The intensities of peaks at 782 cm^-1 (nucleic acids) and 1004 cm^-1 (phenylalanine of protein) did not change evidently even under extremely high ClO₂ concentrations. Thus, ClO₂ rapidly permeates the Nb spore wall, changing the protein secondary structure to lose biological function and destroy permeability, causing trehalose to leak out. These effects are ClO₂ concentration-dependent, but no other obvious changes to biomacromolecules were detected. Single-cell analysis using LTRS is an effective method to monitor the action of chemical sporicides on microbes in real time, providing insight into the heterogeneity of cell stress resistance.