Morphometry of SARS-CoV and SARS-CoV-2 particles in ultrathin plastic sections of infected Vero cell cultures

Abstract

SARS-CoV-2 is the causative of the COVID-19 disease, which has spread pandemically around the globe within a few months. It is therefore of great interest to collect fundamental information about the disease, its epidemiology and treatment, as well as about the virus itself. While the virus has been identified rapidly, detailed ultrastructural analysis of virus cell biology and architecture is still in its infancy. We therefore studied the virus morphology and morphometry of SARS-CoV-2 in comparison to SARS-CoV as it appears in Vero cell cultures by using conventional thin section electron microscopy and electron tomography. Both virus isolates, SARS-CoV Frankfurt 1 and SARS-CoV-2 Italy-INMI1, were virtually identical at the ultrastructural level and revealed a very similar particle size distribution with a median of about 140 nm. SARS-CoV showed a slightly broader size distribution with a few smaller and bigger particles than SARS-CoV-2. The peplomer density was measured using very thin sections and showed a difference between the two virus isolates. SARS-CoV displayed one-third more peplomers per segmental particle volume than SARS-CoV-2. This result complements a previous qualitative finding, using another isolate of the SARS-CoV-2, which was related to a lower productivity of SARS-CoV-2 in cell culture in comparison to SARS-CoV.

Visualization of SARS-CoV-2 Infection Scenes by ‘Zero-Shot’ Enhancements of Electron Microscopy Images

“…As main example image for our method we used a freely available transmission electron microscopy (TEM) image of SARS-CoV-2 viruses in Vero cell cultures (Laue et al, 2020(Laue et al, , 2021. The original image was recorded with 1376 x 1032 pixels with a pixel edge length corresponding to 0.54 nm.…”

SARS-CoV-2 and extracellular vesicles: An intricate interplay in pathogenesis, diagnosis and treatment

“…SARS-CoV-2 would take advantage of these structures to enhance its replication within the infected cell, but also to maximize its multiplicity of infection, and thus its diffusion, to other cells, creating "collective infectious units" as previously described Eymieux et al, 2021b). However, concerning the mechanisms through which SARS-CoV-2 virions inside vesicular structures egress from infected cells and spread towards other cell targets, several hypotheses have been proposed, but there are still discrepancies and further investigations are needed (Klein et al, 2020;Eymieux et al, 2021b;Kumar et al, 2021;Laue et al, 2021;Mendonça et al, 2021). The contribute of EVs in SARS-CoV-2 infection occurs not only at a morphological level, but also functionally.…”

“…However, the exact fusion mechanism between these organelles and the plasma membrane that would allow the virus release in the extracellular space remains unclear. Morphometric and ultrastructure analyses, although still in infancy, have been performed to fill the gap in the knowledge of the SARS-CoV-2 dynamics in its replicative cycle, especially regarding egress events (Klein et al, 2020;Eymieux et al, 2021b;Kumar et al, 2021;Laue et al, 2021;Mendonça et al, 2021). The presence of "exit tunnels", creating a link between viral particles-rich intracellular structures and the extracellular environment, has been proposed (Mendonça et al, 2021).…”

“…The vaccination campaign helped to counteract severe clinical outcomes, but the ability of SARS-CoV-2 to mutate and evade immune responses still implies the need to find new intervention strategies, requiring in turn a deeper understanding of SARS-CoV-2 biology (Boni et al, 2020). Several morphometric studies are ongoing to elucidate SARS-CoV-2 infection mechanisms, especially egress events and cellto-cell spreading that are still poorly characterized (Klein et al, 2020;Eymieux et al, 2021b;Kumar et al, 2021;Laue et al, 2021;Mendonça et al, 2021). According to these, extracellular vesicles (EVs) trafficking seems to be a deeply involved pathway in SARS-CoV-2 infection, contributing to viral replication, immune evasion, egression from infected cells, and spread to other cell targets, through the so-called "replicative organelles" (Pleet et al, 2018;.…”

COVID-19: Auswirkungen auf das zentrale und periphere Nervensystem

“…Durch Darstellung morphologisch intakter Viruspartikel kann weiterhin eine wichtige Validierung der anderen Techniken erfolgen. Additive wie Gerbsäure können die Darstellung der Spikes deutlich verbessern [ 34 ].…”