Figure 2.

Characterization of the CHIKV-7 vaccine virus and 181/25 virus by growth curve and next generation sequencing. (a) Growth curves of CHIKV-7 virus in iDNA-transfected Vero cells (solid line) and of 181/25 virus in infected Vero cells (dashed line). Vero cells were transfected with 1 μg of pCHIKV-7 iDNA plasmid or infected with 10³ PFU of 181/25 virus. Aliquots of growth medium supernatants were collected and the virus was quantitated by direct plaque assay. Virus presence in the growth medium was determined by plaque assay in duplicates. Each data point represents average of three measurements. Standard deviations are indicated. Data at -1 h indicate PFU of 181/25 virus at the start of infection and IC number corresponding to 1 μg iDNA at the start of transfection, respectively. Data from 0 h show PFU/ml. (b) Plaque morphology of CHIKV-7 virus from transfected Vero cells. Average size of total 51 plaques is 4.30±0.93 mm, as measured using magnified image; with five largest plaques 1.37 times larger than the average size. (c) Plaque morphology of 181/25 P1 virus from transfected Vero cells. Average size of total 48 plaques is 5.01±1.78 mm, as measured using magnified image, with five largest plaques 1.78 times larger than the average size. (d) Comparison of sequence coverage and depth of the virus genomes. RNA was isolated from each virus by Trizol LS and sequenced using Illumina HiSeq2000. Sequencing products were assembled to a reference CHIKV 181/25 sequence. The locations of the nonstructural and structural polyproteins are indicated.