I did a transformation of the BL 21 cells with my plasmid DNA but while growing the culture of the competent cells I accidentally mixed it with my starting culture having just the BL 21 cells.
I plated the culture on kanamycin containing plates and got colonies. I know that ideally the cells that have got my plasmid DNA will be the one growing on the plate containing kanamycin. I just want to make sure that they are not the non competent BL 21 cells. How can I do that? I do not want to go for a sequence verification.
BL21 shouldn't have kanamycin resistance.
Just to be sure, try to grow your BL21 (without plasmid) on kanamycin plates. If it doesn't grow, it means that your selection plate do not have any BL21 (without plasmid) colonies (provided the kanamycin plate you used for selection was freshly made and the antibiotic still functional). If it grows, then its possible that there's contamination in your BL21 only cells.
The E. coli BL21 strain hasn't got intrinsic kanamycin resistance basically.
If there isn't any contamination with other kanamicyn resistant plasmids, your strategy will work, and you will definitely have colonies with your plasmid of interest that have grown in kanamicyn-containing plates.
No, BL 21 does'nt have Kanamycin resistance. Other strains (such as RIPL) could have resistances (engineered), but not BL 21. Make sure you use the appropriate control strain.
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