I am concerned there could be a mix up between my samples and I would like to verify I have the right cells labelled. Thus I need your help finding a method of doing so. I have read that nalidixic acid kills BL21 and without affecting DH5alpha cells, however, there is none readily available in my lab.
I am wondering if anyone can suggest any other ways to differenciate between these two cell types!
Thank you,
dh5alpha is a thiamine auxotroph while BL21 is not. You can use minimal media without thiamine and see if you cells grow. If they do grow, they are probably BL21 and if they do not they are probably dh5alpha. Alternatively you can test the ability of the cells to form blue colonies with x-gal and IPTG induction (since dh5alpha are mutants in lacZ only BL21 would be able to make blue colonies). A less robust way to verify (which I do not recommend) would be checking the growth rate of each (dh5alpha will be slower). Another alternative (which is a bit risky due to possibility of contaminating your lab with phages) is to test resistance to T1/T5 phage for which BL21 is resistance due to fhuA2 mutation. Finally you can do PCR and sequencing in specific mutations that are present in one strain but not the other (you can check each genotype to help you decide which mutation to go for if using this approach).
Good Luck!
Hanna
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