What could be the cause of loss of competency in BL21 Competent E. coli cells? I experienced a problem during transformation—the cells were unable to take up the plasmid. The plasmid itself is functional, as it transformed successfully into other competent bacteria. These BL21 cells were stored at −60°C for one month. Could this be the reason for the loss of competency?
The cells are from New England Biolabs (NEB), catalog number C2530H.
If competent E. coli BL21 cells are stored at −60 °C for one month, there will likely be some loss in transformation efficiency, but they may still be usable, depending on: Initial Competency Quality, Aliquot Handling, Freezer Type and Plasmid Type as well as Cells stored at −80 °C can remain competent for 6 months to a year or more with minimal loss but at −60 °C, efficiency can begin to decline within weeks to months, depending on the specific conditions
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