Photoinactivation of MS2 Bacteriophage Is Enhanced by Unrecognized Proteins from Viral Preparations in Clear Suspensions

Light-mediated inactivation of pathogenic microorganisms is vital to engineering water treatment processes and predicting fate and transport in the environment. However, there is high variability in reported viral photoinactivation rates, even in purported sensitizer-free suspensions. Using bacteriophage MS2 as a model, this study explores the impact of progressive inoculant purification processing by centrifugation, filtration, and ultrafiltration, on photoinactivation rates. Faster inactivation kinetics under UVB radiation correlated with greater presence of background proteins as identified via sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Differences in the determined rate constants were large and statistically significant, nearing a 70% increase from the lowest to highest protein presence. Variations remained even after 100× dilution of viral stock preparations. Furthermore, the likely basis was determined to be an indirect inactivation mechanism via sensitization of host or media proteins in the solution background, as evidenced by the inclusion of singlet oxygen scavenger l-histidine, which resulted in a clustering of reaction rates near the ultracentrifuged sample. These experiments highlight the methodological importance of performing and confirming inoculant purification prior to performing photoinactivation experiments, particularly when isolation of the endogenous pathway is important for practical or mechanistic conclusions, while demonstrating the notable contribution of proteins to the exogenous pathway.