TABLE 1.
Main features of competent cell preparation methods
| Prepn methoda | Feature(s) | E. coli strains usedb | Typical TE(s) (CFU/μg)c | Reference or source |
|---|---|---|---|---|
| Chemical methods | ||||
| Hanahan’s method | (i) Recommended by Molecular Cloning: a Laboratory Manual; (ii) purity of reagents and cleanliness of glassware and plasticware affected TE; (iii) few homemade competent cells exceed 108 CFU/μg of plasmid DNA | DH1, MM294, JM108/9, DH5α, DH10B, TOP10, and Mach1 | 106–109 | 19 |
| Inoue’s method | (i) Recommended by Molecular Cloning: a Laboratory Manual; (ii) cells needed to be cultured at 18°C | DH5α (typical) and XL1-Blue | 5 × 107–3 × 108 | 36 |
| TSS | (i) Heat shock not necessary for transformation; (ii) PEG 3350 used to improve transformation efficiency | DH5α and DB3.1 | ~5 × 106 | 21, 33 |
| TSS-HI | (i) Highest TE for chemically competent cells; (ii) other features similar to TSS, except use of heat shock and MnCl2 | BW25113 and its derived strains | ~7 × 109 | This study |
| Commercial competent cells | (i) Some cells prepared by Hanahan method, but prepn methods not described by most manufacturers | Refer to product catalog | 1 × 109–5 × 109 | Thermo/NEB/Promega/Sigma |
| Nanomaterial methods | ||||
| Yuan’s method | More than 8 steps and more than 9 h needed to prepare nanocatalyst | DH5α | 3.53 × 109 | 22 |
| Deshmukh's method | (i) More than 15 steps and more than 15 h needed to prepare nanoparticle-DNA complex; (ii) expensive and toxic reagents needed | DH5α | ~109 | 23 |
| Electroporation | ||||
| Classical electroporation method | (i) Recommended by Molecular Cloning: a Laboratory Manual; (ii) expensive electroporation equipment needed; (iii) DNA reaction mixtures should be desalted for best TE | DH5α, ElectroMAX DH5α, Turbo electrocompetent DH10B | Homemade, >109; commercial, ~1010 | 44 |
| Commercial competent cells | Detailed prepn methods have not been described | Refer to product catalog | >1 × 1010 | Thermo/NEB/Promega/Sigma |
a
TEs higher than 109 CFU/μg were considered high TEs.
b
Only strains listed in the reference paper were recorded. Other cloning strains could also be used to prepare competent cells with high TE unless the strain was defined.
c
Recorded TEs have been mentioned in the associated source or reference.