Frequent Beneficial Mutations during Single-Colony Serial Transfer of Streptococcus pneumoniae
Figure 1
Changes in fitness of S. pneumoniae over single-colony serial transfer.
(A) Relative growth after 24 h of incubation on THY agar plates expressed as the ratio of log2(CFU/colony) for passaged isolates based on 3 replicate measurements for each isolate compared to day 1 control isolates. Symbols represent average fitness values for independently passaged lines ± S.D. The increase in fitness with duration of passage is significant (F[8,185] = 3.65, P = 0.0006), but differences between ΔcomAB and wild-type lines were not significant (F[1,185] = 0.18, P = 0.67). (B) Variance components of fitness measurements based on relative log2(CFU/colony) for serial transfer lines. Among-line variances for passaged strains are shown with squares. Linear regression of the among-line variance against duration of passage is shown by a solid line, with dotted lines indicating 95% confidence intervals. Among-line variances for day 1 control isolates assayed in parallel at each stage of serial transfer are shown with diamonds. Triangles represent within-line variances for passaged strains. Data from wild-type and ΔcomAB lines are pooled. (C) Relative growth on agar plates, as in panel A, for individual isolates after 126 days of serial transfer. The effect of lineage on fitness was significant (F[23,71] = 34.01, P<0.0001). n = 3 for each lineage. (D) Relative growth in THY broth, expressed as the ratio of maximum growth rates for passaged isolates compared to day 1 control isolates, after 126 days of serial transfer. The effect of lineage on fitness was significant (F[22,68] = 4.96, P<0.0001). n = 3. Bars represent mean values ± S.D. The asterisk indicates an isolate that was unable to grow in broth culture.