The rate of acquisition of rpoS mutations in nutrient-limited chemostats. ECOR strains were inoculated into glucose-limited chemostats and culture samples were withdrawn every 24 h for 4 days as previously described . The aerobic chemostat populations were supplied with 0.02% glucose at a pH of 7, a temperature of 37°C and operating at a dilution rate of 0.1 h-1. The lines represent the proportion of wild-type bacteria, and the error bars on points show the standard deviations between two replicate chemostats with each strain. RpoS levels of tested strains (data from Figure 1): ECOR5 (67.1); ECOR50 (14.5); ECOR55 (15.5); ECOR63 (10.5); ECOR66 (90.8); ECOR69 (107.0).