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  • BL21 Competent E. coli


    Chemically competent E. coli cells suitable for transformation and protein expression. This strain does not express the T7 RNA polymerase.


    • 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


    fhuA2 [lon] ompT gal [dcm] ΔhsdS

    Reagents Supplied

    The following reagents are supplied with this product:

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

    Advantages and Features


    • Routine non-T7 expression

    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.
    • 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.


    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)."

    Supporting Documents

    Material Safety Datasheets

    The following is a list of Material Safety Data Sheets (MSDS) that apply to this product to help you use it safely. The following file naming structure is used to name these document files: [Product Name] MSDS. For international versions please contact us at info@neb.com.


    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 info@neb.com or fill out the Technical Support Form for appropriate document.
    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 "Plate and Go" protocol?
    1. Transformation Protocol (C2530)
    2. 5 Minute Transformation Protocol (C2530)
    3. Protocol for Protein Expression Using BL21 (C2530)

    Selection Tools

    Usage Guidelines & Tips