Fate of Microcolonies Developing In Situ

<p>Microcolonies on days 4 and 5 of separate adaptive mutation experiments were sampled by touching with a needle, then the sample was spread on rich X-gal medium and scored for point-mutant or sectored Lac⁺ phenotype (see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020399#s3" target="_blank">Materials and Methods</a>). The microcolonies were then left to grow into visible colonies (∼10⁷ cells), and the colonies sampled again and samples plated to score for sectoring (hatched bars, day 4 microcolony samples; black bars, day 5 microcolony samples). The numbers of each type of colony observed are shown next to the bars. One single stable microcolony produced a mixed visible colony, which may have been caused by overlap with another colony or microcolony.