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

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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.

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  1. SciScore for 10.1101/2020.08.20.259531: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Experimental Models: Cell Lines
    SentencesResources
    Virus isolates: The following virus isolates were used: Cell culture: Vero E6 cells (African green monkey kidney epithelial cell, ECACC, ID: 85020206) were cultivated in cell culture flasks with D-MEM, including 1% L-glutamine and 10% fetal bovine serum, for 1 d at 37°C and 5% CO2 to reach approximately 70% confluence.
    Vero E6
    suggested: None
    Software and Algorithms
    SentencesResources
    Alignment of the tilt series (using 10 nm colloidal gold fiducials) and reconstruction of the tomograms were performed with the IMOD software package21 (version 4.9.12) using SIRT with 25 iterations after low pass filtering (cut off = 0.35, low pass radius sigma = 0.05) of the aligned image stack.
    IMOD
    suggested: (IMOD, RRID:SCR_003297)
    The volume containing the selected particle was extracted, filtered to increase contrast (Normalize local contrast; maximum pixel size, SD = 5, stretched and centered histogram) and resliced in z to a resolution of 1.5 nm using Fiji.
    Fiji
    suggested: (Fiji, RRID:SCR_002285)

    Results from OddPub: Thank you for sharing your data.


    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    Results from TrialIdentifier: No clinical trial numbers were referenced.


    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.


    Results from JetFighter: We did not find any issues relating to colormaps.


    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • No funding statement was detected.
    • No protocol registration statement was detected.

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