I am going to prepare competent Escherichia coli for use in transformation. Usually, when I conduct a starter culture and overnight culture, I add ampicillin. However, in the protocol, they did not mention adding ampicillin. Should I follow the protocol as is, or should I add ampicillin to the LB broth?
Well, it depends on which strain you are going to use. As for DH5a and Bl21, no antibiotics shall be added, for other strains you should check the literatures. However, antibiotics are added when transforming these competents with plasmids containing antibiotic resistance gene.
Dear Mnor Faleh
did you add ampicillin on the overnight cultures of trasformed cells or empty cells, since in general the plasmid carry an antibiotic resistance (ampicillin) and it confer the ability to growth in the presence of the antibiotic to the transformed bacteria while the empty cells in absence of the plasmid will die if the antibiotic is added.
However there are some strain as Rosetta, Origami which due to presence of an additional plasmid or a resistance antibiotic cassete integrated in the genome to generate a gene knockout strains that are able to growth in presence of specific antibiotics and therefore in this case you can add this specific antibiotic during the competent cells preparation.
best regards
Manuele
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