Facile Control of a Tailed Virus Surrogate by Iron Conventional Coagulation and Electrocoagulation

Both FeCl₃ conventional coagulation and Fe(0) electrocoagulation were highly effective in mitigating the long-tailed somatic phage P1. We targeted enterobacterial coliphages because they are better than fecal indicator bacteria in tracking environmental persistence of viral pathogens and their fate in wastewater unit operations. Cryogenic electron microscopy (cryo-EM) of intact/damaged P1 and enumeration of infective virions by plaque assays demonstrated control via both removal and inactivation. Cryo-single particle analysis was coupled with cryo-electron tomography to generate 3-dimensional electron density maps to visualize and analyze untreated and coagulated capsids. To our knowledge, this is the first report of cryo-EM to visualize structurally damaged viruses with environmental relevance. Viruses were intrinsically enmeshed in precipitates consistent with sweep coagulation. Direct evidence of multiple inactivation mechanisms was obtained including (i) capsid breakage leading to leakage of viral genome and other components, (ii) deformation and thinning of capsid proteins, (iii) severance/damages to the neck region where the tail is attached to the capsid, (iv) removal, fragmentation, and splintering of tail sections, and (v) baseplate damage (including receptor-binding proteins). Conformational alterations to proteins, changes to secondary structures, and specific interactions with flocs were inferred from infrared spectroscopy for both coagulation approaches. However, only electrocoagulation oxidized proteins. Extremely facile reduction of P1 suggested that coliphages with myovirus morphology may not be conservative surrogates to measure log reduction values for regulatory purposes and public health protection by iron conventional coagulation and electrocoagulation.