The concentration of the K. mikimotoi recombinant plasmid
solution was estimated by measuring the optical density at 260 nm.
A series of plasmid standard samples (approximately 10–107 copies
of recombinant plasmid) was prepared by 10-fold dilution of the K.
mikimotoi recombinant plasmid solution. Meanwhile, the genomic
DNA of quantified K. mikimotoi cells was extracted, and a series of cell
standard samples (approximately 1–104 cells) was prepared by 10-
fold dilution of the crude DNA solution.
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.