Product Class: Competent Cell

BL21 Competent E. coli

NEB does not add a dry ice surcharge to our competent cell shipments.
Catalog #SizeConcentration
C2530H20 x 0.05 ml/tube



  • Transformation efficiency: 1–5 x 107 cfu/μg pUC19 DNA
  • Routine non-T7 expression
  • Deficient in proteases Lon and OmpT
  • Resistant to phage T1 (fhuA2)
  • B Strain
  • Free of animal products
Chemically competent E. coli cells suitable for transformation and protein expression. This strain does not express the T7 RNA polymerase.


  • Routine non-T7 expression


fhuA2 [lon] ompT gal [dcm] ΔhsdS

Reagents Supplied

The following reagents are supplied with this product:

Store at (°C)Concentration
pUC19 Vector-200.05 ng/μl
SOC Outgrowth Medium41X

Properties and Usage

Antibiotics for Plasmid SelectionWorking Concentration
Ampicillin100 μg/ml
Carbenicillin100 μg/ml
Chloramphenicol33 μg/ml
Kanamycin30 μg/ml
Streptomycin25 μg/ml
Tetracycline15 μg/ml

Storage Temperature


Shipping Notes

  • Ships on dry ice

Quality Control

Quality Control Assays

The following Quality Control Tests are performed on each new lot and meet the specifications designated for the product. Individual lot data can be found on the Product Summary Sheet/Datacard or Manual which can be found in the Supporting Documents section of this page. Further information regarding NEB product quality can be found here.
  • Transformation Efficiency:
    The competent cells are tested for transformation efficiency and pass minimum release criteria. Transformation efficiency is defined as the number of colony forming units (cfu) which would be produced by transforming 1 μg of plasmid into a given volume of competent cells.

Supporting Documents

The Certificate of Analysis (COA) is a signed document that includes the storage temperature, expiration date and quality control's for an individual lot. The following file naming structure is used to name these document files: [Product Number]_[Size]_[Version]_[Lot Number]
The Specification sheet is a document that includes the storage temperature, shelf life and the specifications designated for the product. The following file naming structure is used to name these document files: [Product Number]_[Size]_[Version]
The following is a list of Safety Data Sheet (SDS) that apply to this product to help you use it safely.
The Product Summary Sheet, or Data Card, includes details for how to use the product, as well as details of its formulation and quality controls. The following file naming structure is used to name the majority of these document files: [Catalog Number]Datasheet-Lot[Lot Number]. For those product lots not listed below, please contact NEB at or fill out the Technical Support Form for appropriate document.


  1. CAUTION: This product contains DMSO, a hazardous material. Review the MSDS before handling.
  2. STORAGE AND HANDLING: Competent cells should be stored at -80°C. Storage at -20°C will result in a significant decrease in transformation efficiency. Cells lose efficiency whenever they are warmed above -80°C, even if they do not thaw.
    Note: Expression from vectors containing a T5-lacO promoter will not be regulated unless the expression vector encodes the lacI gene or a compatible vector expresses LacI or the host strain overproduces LacI (e.g NEB #C3037 NEB Express Iq Competent E. coli)."
  1. Does New England Biolabs offer strains of Competent E.coli suited for protein expression?
  2. What are the solutions/recipes (C2530)?
  3. What are the strain properties (C2530)?
  4. Why are there no colonies or no growth in liquid culture (C2530)?
  5. Why is the induced protein insoluble (C2530)?
  6. Why is there no protein visible on gel or no activity (C2530)?
  7. Can I store competent cells at -20°C instead of -80°C?
  8. Which kind of transformation tubes should be used?
  9. What volume of DNA can be added into competent cells?
  10. What is the shelf life for this strain (NEB #C2350H)?
  11. Are NEB's competent cells compatible with the “Mix & Go" protocol?
  12. What is the difference between BL21 and BL21(DE3) competent E.coli cells?
  13. How should I store SOC Outgrowth Medium? The SOC I received with my competent cells recommends storage at either room temperature or 4°C, however, when I purchase it as a stand alone product, it recommends storing it at 4°C. Which is better?
  1. Transformation Protocol (C2530)
  2. 5 Minute Transformation Protocol (C2530)
  3. Protocol for Protein Expression Using BL21 (C2530)