Product Class: Competent Cell

dam-/dcm- Competent E. coli

NEB does not add a dry ice surcharge to our competent cell shipments
Catalog #SizeConcentration
C2925I6 x 0.2 ml/tube
C2925H20 x 0.05 ml/tube



  • Grow plasmids free of Dam and Dcm methylation
  • Free of animal products
  • Phage T1 resistant (fhuA31)
  • Transformation efficiency: 1-3 x 106 cfu/μg pUC19 DNA
  • Activity of nonspecific endonuclease I (endA1) eliminated for highest quality plasmid preparations
  • K12 Strain
Methyltransferase deficient chemically competent E. coli cells suitable for growth of plasmids free of Dam and Dcm methylation. Note that dam- strains are not recommended as a host for primary cloning/ligation. The dam mutation can result in an increased mutation rate in the cell and a reduction in the transformation efficiency. DNA should be maintained in a dam+ strain unless there is a specific need for DNA free of Dam or Dcm methylation.


  • Dam/Dcm methyltransferase free plasmid growth


ara-14 leuB6 fhuA31 lacY1 tsx78 glnV44 galK2 galT22 mcrA dcm-6 hisG4 rfbD1 R(zgb210::Tn10) TetS endA1 rspL136 (StrR) dam13::Tn9 (CamR) xylA-5 mtl-1 thi-1 mcrB1 hsdR2

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


Effect of heat shock time on dam-/dcm- competent E. coli transformation efficiency: 50 μl of competent cells were transformed with 100 pg of pUC19 control DNA following the provided High Efficiency Transformation Protocol except heat shock time varied from 0 to 80 seconds.
Effect of DNA incubation time on dam-/dcm- competent E. coli transformation efficiency: 50 μl of competent cells were transformed with 100 pg of pUC19 control DNA following the provided High Efficiency Transformation Protocol except DNA incubation time varied from 0 to 40 minutes.
Effect of outgrowth medium on transformation efficiency: 50 μl of -/dcm-competentE.coli was transformed with 100 pg of pUC19 control DNA following the provided High Efficiency Transformation Protocol with the exception of varying the outgrowth medium. NEB SOC outgrowth medium delivers the highest transformation efficiency.

Properties and Usage

Antibiotics for Plasmid SelectionWorking Concentration
Ampicillin100 μg/ml
Carbenicillin100 μg/ml
Kanamycin30 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.

Supporting Documents

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.
  1. Can I transform unmethylated DNA into dam-/dcm- competent E.coli (C2925)?
  2. Does New England Biolabs offer a methyltransferase free strain of Competent E.coli?
  3. How long should I incubate cells on ice after DNA has been added (NEB #C2925H and NEB #C2925I)?
  4. Is dam-/dcm- (NEB #C2925H/C2925I) resistant to kanamycin?
  5. Is the DNA yield lower using dam-/dcm- strain (C2925)?
  6. What are the solutions/recipes (C2925)?
  7. What are the strain properties (C2925)?
  8. What is the difference between NEB #C2925H and NEB #C2925I?
  9. What is the optimal heat shock time for this strain (NEB #C2925H and NEB #C2925I)?
  10. Which strain of Competent E. coli should I use for general cloning?
  11. Why were the colonies at different size after transformation of dam-/dcm- competent E.coli (C2925)?
  12. How should I calculate the transformation efficiency (C2925)?
  13. Can I store competent cells at -20°C instead of -80°C?
  14. Which kind of transformation tubes should be used?
  15. What volume of DNA can be added into competent cells?
  16. What is the shelf life for this strain (NEB #C2925H and NEB #C2925I)?
  17. Are NEB's competent cells compatible with the "Plate and Go" protocol?
  1. 5 Minute Transformation Protocol (C2925)
  2. Transformation Protocol (C2925)

Application Notes