Plasmid pCdiBAI becomes fixed in populations after long-term passage.

<p><b>A</b>) Three <i>E</i>. <i>coli</i> EPI100 pCdiBAI lineages were passaged for 500 cell generations, and the percentage of cells that carry plasmid pCdiBAI determined. <b>B</b>) Total DNA was isolated from the lineages shown in panel A after 500 generations (g500). DNA samples were digested with PstI and analyzed by Southern blot using radiolabeled probes specific for plasmid pCdiBAI and the <i>groL</i> chromosomal locus. Control samples isolated from cells lacking plasmid (F-), cells carrying pOri_F and unpassaged cells carrying pCdiBAI (pCdiBAI^g0) were also analyzed. Molecular standards were generated by PCR of plasmid pCdiBAI and the genomic <i>groL</i> locus. <b>C</b>) Plasmid DNA was isolated from the lineages in panel A after 0 (g0), 100 (g100), 200 (g200) and 300 (g300) generations. The plasmids were transformed into <i>E</i>. <i>coli ΔbamA</i>::<i>cat</i> pZS21-BamA^ECL and the percentage of cells carrying plasmid pCdiBAI was monitored over 100 generations.