FIG 1 .

Changes in growth rate and morphology during the evolution of ΔccrM populations in rich medium. Twelve independent ΔccrM populations and 10 independent wild-type (NA1000) populations were transferred from minimal medium (M2G) to rich medium (PYE) at an OD₆₆₀ of 0.01 at the beginning of the experiment. Each second day for the first 40 doublings and each day for the following doublings, the culture was rediluted to an OD₆₆₀ of 0.001. (A) Changes in average overnight generation time during the course of the experiment for the 12 ΔccrM populations and for the 10 NA1000 control populations. The overnight generation time was measured, taking the initial and final OD₆₆₀ and time interval into account. The error bars show standard deviations from the means for the 10 or 12 populations of each starting genotype. (B) Morphology of representative cells in a ΔccrM population during the initial phase of evolution: before transfer to rich medium (M2G) and 6, 15, and 32 generations (gen.) after transfer. After 6 generations in rich medium, cells formed 10- to 40-µm-long filaments that did not show signs of lysis; after 15 generations, more than 50% of the filamentous cells seemed to lyse (light grey cells); after 32 generations, viable shorter cells invaded the population. (C) Between generation 50 and generation 300, the clones sampled from the ΔccrM populations gained in fitness (growth rate). Two clones were isolated from each of the 12 ΔccrM populations at generation 50 and generation 300 and grown independently in rich medium. The doubling times were measured in exponential phase. The thick line represents the median, the limits of the box show the 25th and 75th quartiles, and the whiskers show the 5th and 95th quantiles.