Strain Properties

There are many properties to consider when choosing a strain for your experiments. Requirements such as plasmid preparation, blue/white screening, cytoplasmic disulfide bond formation, and fast colony growth necessitate specific strain choices. The following selection chart highlights the characteristics of NEB’s strains to help select the optimal strain for a particular experiment.

CAUTION: Chemically Competent E. coli contain DMSO, a hazardous material. Review the MSDS before handling.

Product NEB # Transform
Efficiency
(cfu/µg)(1)
Strain T1 Phage Resistant Library Construc-
tion(2)
Cloning/
Sub
Cloning
Blue/
White
Screening
laclq lysY endA¯(3) Protease
Deficient(4)
F' recA¯ T7 RNA Polymerase Cytoplasmic
disulfide
bond
formation(5)
Drug
Resistance(6)
Cloning Strains
NEB® Turbo Competent E. coli (High Efficiency) 1-3x109 K12 nit
NEB® 5-alpha Competent E. coli (High Efficiency) 1-3x109 K12 none
NEB® 5-alpha F' Iq Competent E. coli (High Efficiency) 1-3x109 K12 tet
NEB® 10-beta Competent E. coli (High Efficiency) 1-3x109 K12 str
dam-/dcm- Competent E. coli 1-3x106 K12 cam, str, nit
NEB® Stable Competent E. coli (High Efficiency) 1-3 x 109 K12 tet, str
Protein Expression Strains
NEB® Express Competent E. coli (High Efficiency) 0.6-1x109 B nit
NEB® Express Iq Competent E. coli (High Efficiency) 0.6-1x109 B cam, nit
T7 Express Competent E. coli (High Efficiency) 0.6-1x109 B nit
T7 Express lysY Competent E. coli (High Efficiency) 0.6-1x109 B cam, nit
T7 Express lysY/Iq Competent E. coli (High Efficiency) 0.6-1x109 B cam, nit
SHuffle® T7 Competent E. coli 1 x 106 K12 str, spec, nit
SHuffle® Express Competent E. coli 1 x 107 B spec(7), nit
SHuffle® T7 Express Competent E. coli 1 x 107 B spec(7), nit
SHuffle® T7 Express lysY Competent E. coli 1 x 107 B Cam, spec(7), nit
BL21(DE3) Competent E. coli 1-5x107 B
Lemo21(DE3) Competent E. coli 1-3x107 B cam
BL21 Competent E. coli 1-5x107 B
NiCo21(DE3) Competent E. coli 1-5x107 B
  1. TE given are for high-efficiency chemically competent strains. TE for electrocompetent strains are 1-4 x 1010cfu/mg. TE for subcloning strains are >1 x 106.
  2. Restriction-deficient strain.
  3. Important for plasmid preparation.
  4. Lacks Lon and OmpT protease activity
  5. Constitutively expresses a chromosomal copy of the disulfide bond isomerase DsbC.
  6. nit = nitrofurantoin, tet = tetracycline, cam = chloramphenicol, str = streptomycin, spec = spectinomycin
  7. Resistance to low levels of streptomycin may be observed.
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