Mutational dynamics of the SARS coronavirus in cell culture and human populations isolated in 2003

Vega, Vinsensius B; Ruan, Yijun; Liu, Jianjun; Lee, Wah Heng; Wei, Chia Lin; Se-Thoe, Su Yun; Tang, Kin Fai; Zhang, Tao; Kolatkar, Prasanna R; Ooi, Eng Eong; Ling, Ai Ee; Stanton, Lawrence W; Long, Philip M; Liu, Edison T

First, we sought to determine the rate of mutation of the SARS-CoV in Vero cell culture. To achieve this, we subjected SIN2774 isolate to 5 passages in Vero cells. At the appearance of cytolysis at each passage samples were withdrawn and their genomes completely sequenced. Any ambiguities by capillary sequencing were clarified by mass spectroscopic validation [6] . Our results showed that the Vero cell passages are actually comprised of two coexisting quasispecies bearing either an A or G at position 18372. No mutations emerged upon passage, and the ratio of A/ G at 18372 remained constant over the passages (Table 1) . This suggests that the mutation rate in culture of SARS-CoV is very low at <1 in 5 passages. Thus artificial mutations from limited in vitro cell culture are negligible.