Inoculate a starter culture of E. coli containing the plasmid in LB medium containing the appropriate selective antibiotic.
Grow overnight at 37°C with appropriate shaking (e.g., 200–250 RPM).
Main Culture Expansion
Dilute the overnight starter culture into the main volume of rich LB medium (e.g., 1:100 dilution) supplemented with the selective antibiotic.
Incubate at 37°C with shaking until the culture enters the mid-to-late log phase, generally indicated by an OD600 of 0.6 to 0.8.
Low-Concentration Amplification
Add the chloramphenicol stock solution to the flask to achieve a reduced, specific concentration intended for partial inhibition (10–20 µg/mL).
Incubate the culture for an extended period, 14 to 16 hours (overnight). This extended time allows for the natural degradation of existing Rop protein.
Literature References
Frenkel, L., & Bremer, H. (1986). Increased amplification of plasmids pBR322 and pBR327 by low concentrations of chloramphenicol. DNA, 5(6), 539–544. (main reference)