Figure 3.

Delta spike P681 reversion impairs viral fitness

(A) Construction of revertant Delta-P681 SARS-CoV-2. Single nucleotide G-to-C substitution was engineered into the Delta variant to construct Delta-P681 SARS-CoV-2.

(B) Plaques of Delta-P681 virus. The plaque images were taken on day 2.5 post infection of Vero E6 cells. The average diameter of the plaques are presented in the parentheses. For direct comparison of plaque sizes of different viruses, all plaques presented in different figures of this paper were performed from the same set of experiment.

(C and D) Replication competitions between Delta and Delta-P681 (C) and Delta-P681 and Alpha (D) on HAE cultures. Equal PFU inputs of two viruses were mixed and inoculated onto HAE cultures at an MOI of 5. After 2 h incubation, the cells were washed thrice with DPBS and maintained for 5 days. Secreted progeny viruses were collected daily by incubating the apical side of the HAE culture with 300 μL DPBS at 37°C for 30 min. Red dots represent individual cell cultures (n = 6) pooled from 2 independent biological repeats; the horizontal lines in each catseye represent the mean; shaded regions represent standard error of the mean; y axes use a log₁₀ scale. Black numbers above each set of values (catseye) indicate the ratios of two viral RNA species. p values were calculated for group coefficient using linear regression model. ^∗∗p < 0.01, ^∗∗∗p < 0.001.