Quantification of pBR322 plasmid copy number by digital droplet PCR.

<p><i>E</i>. <i>coli</i> DH5α total DNA isolated by the bead beating method (A) and the QIAamp DNA mini kit (B), from two independent bacterial cultures in a logarithmic growth phase (Experiment 1 and 2), served as a template for the <i>bla</i> and <i>dxs</i> ddPCR amplification with the use of primer set A (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169846#pone.0169846.t001" target="_blank">Table 1A</a>). Each experiment was run in two replicates (bla1, bla2 and dxs1, dxs2). Error bars indicate the 95% confidence limits as determined from the Poisson distribution. (C) Columns A01 and E01 represents single wells of ~ 20,000 droplets after ddPCR amplification of <i>bla</i> and <i>dxs</i>, respectively. (D) Estimated pBR322 copy number by digital droplet PCR. The plasmid copy number of pBR322 was calculated by dividing the copy number of <i>bla</i> by the copy number of <i>dxs</i>. Average PCN from four measurements was determined to be 20.5 for QIA and 7.3 for the bead-beating method.