Two standard curves were established with the threshold cycle
(Ct) values against the denary logarithms of the recombinant
plasmid copy numbers (lgNplasmid) or cell numbers (lgNcell). Each
standard sample concentration was run in triplicate. The correlative
plasmid copy numbers of the cell samples were calculated
from the two standard curves. Finally, a regression curve was
created by plotting the cell numbers and the corresponding
plasmid copy numbers.