Figure 3
Determination of plasmid copy number. Quantitative PCR (qPCR) was used to detect the copy number of plasmid pJGW07 in relation to the chromosome. Shown are the results after the fifth passage through A) selective and B) non-selective media. The x-axis is the number of iterations of the polymerase chain reaction, and the y-axis displays the logarithm of ΔRn, which is the fluorescence of the SYBR green dye with the baseline fluorescence subtracted. The number of cycles required to cross a given threshold (cycles to threshold or Ct) is reflective of the plasmid copy number (PCN). The threshold is indicated by a horizontal line. PCN was calculated using the formula PCN = 2^| Ctchromosome— Ctplasmid |. The copy number ranged from about 25 to 115 copies per chromosome in the cultures with selective media. The copy number was determined based on two independent biological samples with three technical replicates (Additional file 1: Table S1).