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 necessary 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 100 nm without spikes. Maximal spike length of both viruses was 23 nm. The number of spikes per virus particle was about 30% higher in the SARS-CoV than in the SARS-CoV-2 isolate. This result complements a previous qualitative finding, which was related to a lower productivity of SARS-CoV-2 in cell culture in comparison to SARS-CoV.

Innovative Approach to Fast Electron Microscopy Using the Example of a Culture of Virus-Infected Cells: An Application to SARS-CoV-2

“…For example, SARS-CoV-2-infected Vero E6 cells were seen to be interconnected by microvilli (Figure 5E,F and Figure 6E-H). These microvilli were en-riched with numerous SARS-CoV-2 particles (Figure 4F,I), as already described [9,18,20,22]. We showed here that not only the apical microvilli were enriched in SARS-CoV-2 particles, but also those that could be the intercellular baso-lateral microvilli.…”

“…With our new methodology, we observed the previously described [9] round to hexagonal electron-dense SARS-CoV-2 particles, around 80 nm in diameter and more or less spiky, depending on their location (Figure 2). We also obtained previously described ultrastructural features of the SARS-CoV-2-infected cells [9,[17][18][19][20][21][22]: neo-virions formed in the peri-nuclear region from budding of the endoplasmic reticulum-Golgi apparatus complex, with a formation of morphogenesis matrix vesicae, and new particles expelled from the cells through cell lysis or by fusion of virus-containing vacuoles with the cell plasma membrane (Figures 3-7). With our new methodology, we observed the previously described [9] round to hexagonal electron-dense SARS-CoV-2 particles, around 80 nm in diameter and more or less spiky, depending on their location (Figure 2).…”

Microscopic Observation of SARS-Like Particles in RT-qPCR SARS-CoV-2 Positive Sewage Samples

“…Our approach allowed us to get images of SARS-CoV-2 virus-like particles in RT-qPCR SARS-CoV-2 positive sewage samples. Indeed, the objects tagged by anti-SARS-CoV-2 fluorescence appeared by SEM to be compatible in size and shape with those of coronavirus virions previously described [ 29 , 30 , 37 ].…”

SARS-CoV-2 Portrayed Against HIV: Contrary Viral Strategies in Similar Disguise

“…Demographic features geographic origin West-Central Africa (Cameroon, DR Congo) China (Wuhan) [5,6] first recorded case HIV-1: 1959 (DR Congo) SARS-CoV-2: Nov. 17, 2019 (China) [7][8][9][10] AIDS: 1981 (USA) COVID-19: Dec. 31, 2019 (China) est. time of origin/cross-species transmission 1920s October/November 2019 [7,[11][12][13] animal source non-human primates primary host: bats, intermediate hosts: small mammals; yet unconfirmed [5,[14][15][16] active [6,22,23] number of spikes per virus 7-14 15-40 [23][24][25] spike size (height × width) 12 × 15 nm 20 × 13 nm [26][27][28][29] spike amino acids 856 1273 [30,31] potential N-glyco sites per spike monomer 31 (HxB2) 22 (Wuhan-Hu-1) [30,31] spike proteolytic cleavage sites 1 2 [32,33] capsid Conical (many hexagons and 12 pentagons of subunits) helical [34][35][36] genome (+)ssRNA, diploid dsDNA genome intermediate (+)ssRNA, haploid [37,38] genome size 9.7 kb (one of the smallest viral genomes) 29.7 kb (one of the largest viral genomes) [30,31] evolution rate proviral DNA: 4 × 10 −3 per base per cell (1 mutation every 250 base pairs) 1 × 10 −3 per base per year (2 mutations per month) [12,39,…”