Why did E. coli grow on both the P- and P+ sides of the LB plate?

Why did E. coli grow on both the P- and P+ sides of the LB plate?

• A. The LB plate provided nutrients for all cells regardless of plasmid.
• B. Only P+ cells could grow due to plasmid.
• C. P- side had no nutrients.
• D. The plate had a selective color indicator.

Answer: (A)

On a nutrient-rich LB plate, bacteria can grow regardless of whether they carry a plasmid. The plasmid isn’t providing nutrients, so without any selection pressure (like an antibiotic), both plasmid-containing and plasmid-free cells have access to the same nutrients in the medium and can form colonies. The presence or absence of the plasmid only matters when a selective agent or specific marker is used. Since the plate is just LB, it supports growth of both P- and P+ cells.

On a nutrient-rich LB plate, bacteria can grow regardless of whether they carry a plasmid. The plasmid isn’t providing nutrients, so without any selection pressure (like an antibiotic), both plasmid-containing and plasmid-free cells have access to the same nutrients in the medium and can form colonies. The presence or absence of the plasmid only matters when a selective agent or specific marker is used. Since the plate is just LB, it supports growth of both P- and P+ cells.