Heteroaggregation of an enveloped bacteriophage with colloidal sediments and effect on virus viability

Abstract

Four sediments in the colloidal size range: goethite, montmorillonite, illite, and kaolinite, were suspended with the bacteriophage φ6, a model enveloped virus, to determine relative rates of heteroaggregation and the effect of aggregation on virus viability. Turbidity was measured on combinations of virus and each sediment type at low concentration to determine aggregation rates. Aggregation of sediment with virus occurred regardless of mineral type, and larger fraction of virus is expected to aggregate with increasing sediment concentration leading to higher deposition rates. The negatively charged sediments, aggregated with φ6 (also negatively charged at neutral pH) at a faster rate than the positively charged sediments, yielding turbidity slopes of 4.94 × 10^-3 s^-1 and 7.50 × 10^-4 s^-1 for φ6-montmorillonite and φ6-illite aggregates, respectively, and 2.98 × 10^-5 s^-1 and 2.84 × 10^-5 s^-1, for φ6-goethite and φ6-kaolinite, respectively. This indicates that the interaction between sediments and virus is hydrophobic, rather than electrostatic. Large numbers of virions remained viable post-aggregation, despite the fragility of the viral envelope, indicating that small-sized aggregates, which may travel more readily through porous media, may pose an infection risk. The fraction of φ6 that remained viable varied with sediment type, with montmorillonite-φ6 aggregates experiencing the greatest reduction in infectivity at 35%. TEM analyses reveal that in all sediment-φ6 combinations, infectivity loss was likely due to disassembly of the viral envelope as a result of aggregation.

Keywords: Aggregation; Bacteriophage; Clay minerals; Montmorillonite; Virus.

Graphical abstract

Fig. 1

Turbidity (λ = 750 nm) of sediments in reduced cation buffer for (A) Goethite; (B) Illite; (C) Kaolinite; and (D) Montmorillonite.

Fig. 2

Time evolution of turbidity (λ = 750 nm) for heteroaggregation of φ6 with (A) Goethite; (B) Illite; (C) Kaolinite; and (D) Montmorillonite. Linear fits for goethite and kaolinite are shown as gray diamonds.

Fig. 3

Time evolution of turbidity (λ = 750 nm) at early time with linear fits (gray diamonds) for φ6-Montmorillonite and φ6-Illite heteroaggregates.

Fig. 4

A) SDS-PAGE of ϕ6 in pellets and supernatants. Lanes are: 1) Marker; 2) Purified ϕ6; 3) ϕ6 — montmorillonite aggregate supernatant; 4) ϕ6 — montmorillonite aggregate pellet; 5) ϕ6 — Kaolinite aggregate supernatant; 6) ϕ6 — Kaolinite aggregate pellet; 7) ϕ6 — Illite aggregate supernatant; 8) ϕ6 — Illite aggregate pellet; 9) ϕ6 — Goethite aggregate supernatant; 10) ϕ6 — Goethite aggregate pellet. B) Density trace of SDS-PAGE for protein band P1, corresponding SDS-PAGE lanes are shown on top of plot. Relative density of pellet and supernatant P1 bands show that the majority of virions are in aggregates.

Fig. 5

A) Viable φ6 populations in pellet and supernatant: B) Percentage distribution of virions between pellets and supernatants.

Fig. 6

TEM Micrograph of heteroaggregates of φ6 and A) Goethite, C) Kaolinite and D) Montmorillonite. Insets show enlarged view (contrast (enhanced) of individual virions in the aggregates. φ6 viruses in the aggregates demonstrate significant distortion as compared to isolated φ6.