Montmorillonite-mediated aggregation induces deformation of influenza virus particles

• Influenza virus readily aggregates with montmorillonite particles.
• Influenza virus particles flattened against montmorillonite faces to increase contact area.
• Virions were predominantly adsorbed to negatively charged platelet faces.
• Influenza virus infectivity was not compromised despite aggregation and deformation.

The interaction between influenza virus [subtype A/Puerto Rico/8/1934 H1N1, (PR8)] and montmorillonite (Mt) is investigated by transmission electron microscopy and biochemical methods to determine how PR8 morphology and viability is affected. The majority of the PR8 particles formed aggregates with the Mt. TEM analysis showed that the virus particles retained structural integrity after aggregation but exhibited changes in morphology when compared to isolated PR8 and Mt aggregated with bromelain-treated PR8 (surface glycoproteins removed). Virus deformation shows that the virions exhibit an attraction to the Mt faces, possibly through hydrophobic interaction. The mean projection area of the aggregated PR8 was (10.4 ± 6.1) × 103 nm2 compared to (9.5 ± 3.3) × 103 nm2 for PR8 missing the surface glycoproteins; and (8.0 ± 3.9) × 103 nm2 for non-aggregated PR8 controls. The increase in projection area of the aggregated PR8 suggests that the viruses deformed to increase contact region with the Mt faces with a subsequent compression normal to the face. PR8 missing the surface protein also exhibited an increase in projection area, although to a lesser extent, indicating that both the surface glycoproteins and viral envelope are attracted to the Mt faces. Circularity calculations indicate that the aggregated PR8 (circularity: 0.69 ± 0.16) are less round, i.e. more distorted, than either control PR8 (0.78 ± 0.14) or aggregated PR8 without surface glycoproteins (0.76 ± 0.12). The pleomorphic nature of influenza virus may allow it to survive the deformation induced by the Mt platelets. High resolution TEM micrographs revealed that the otherwise-round viruses flattened when in contact with platelet faces, thus increasing contact area with the Mt.The PR8 was found to remain infectious after aggregation although at a lower rate than PR8 controls. The apparent reduced infectivity is likely a result of each aggregate (containing ~ 102 viral particles) acting as a single infectious unit.

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