Article Title: Rescue of SARS-CoV-2 from a Single Bacterial Artificial Chromosome
Figure Lengend Snippet: Characterization of rSARS2-CoV-2 in vitro . (A and B) Genotypic characterization. Vero E6 cells were mock infected or infected (MOI, 0.01) with rSARS-CoV-2 or the SARS-CoV-2 USA-WA1/2020 natural isolate. At 24 h postinfection, total RNA from Vero E6 cells was extracted and a 1,297-bp region of the M gene (nt 26488 to 27784) was amplified by RT-PCR. Amplified DNA was subjected to MluI digestion ( Fig. 1 ). (A) Undigested (top) and digested (bottom) samples were separated in a 0.7% agarose gel. The RT-PCR-amplified DNA product was also sequenced to verify the presence of the silent mutation in the MluI restriction site introduced in the viral genome of the rSARS-CoV-2 ( Fig. 1 ). (B) The MluI restriction site is underlined in red, and the silent mutation introduced to remove the MluI restriction site (T to A) is shown in the black box. (C) Verification of BAC and rSARS-CoV-2 sequences. The SARS-CoV-2 non-reference allele frequency was calculated by comparing short reads to the reference genome of the USA-WA1/2020 reference. All variants were at low frequency in the P6 natural isolate (top), the BAC (bottom), and rSARS-CoV-2 (middle), with the exception of introduced variants at positions 21895 and 26843, which were fixed in the BAC and in rSARS-CoV-2. Non-reference alleles present in less than 1% of reads are not shown. (D) Plaque phenotype. Vero E6 cells were infected with ∼20 PFU of rSARS-CoV-2 (left) or the natural SARS-CoV-2 isolate (right). After 72 h of incubation at 37°C, cells were fixed and immunostained with the N protein 1C7 monoclonal antibody. (E) Growth kinetics. Vero E6 cells were infected (MOI, 0.01) with rSARS-CoV-2 or the natural SARS-CoV-2 isolate. At the indicated times postinfection, tissue culture supernatants were collected and viral titers were assessed by plaque assay (PFU/ml). Data are presented as means ± SDs. LOD, limit of detection.
Article Snippet: The SARS-CoV-2 USA-WA1/2020 natural isolate was obtained from BEI Resources (NR-52281) and amplified on Vero E6 cells.
Techniques: In Vitro, Infection, Amplification, Reverse Transcription Polymerase Chain Reaction, Agarose Gel Electrophoresis, Mutagenesis, BAC Assay, Incubation, Plaque Assay