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RbCl Super Competent Cells   

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This method is used to inexpensively prepare home-made competent cells of E. coli. The transformation efficiency is at the high end of chemical-efficient competent cells, and close to library-efficient competent cells.

Keywords: Competent cells, E. coli, Chemical competent cells, Rubidium chloride

Materials and Reagents

  1. 3 mM hexamine cobalt chloride
  2. Tryptone 
  3. Yeast extract
  4. NaCl
  5. DMSO
  6. KCl
  7. MgCl2
  8. MgSO4
  9. KOH
  10. CaCl2·2H2O
  11. RbCl
  12. SOB or 2x YT (see Recipes)
  13. MES (see Recipes)
  14. TFB (50 ml) enough for 80 tubes/400 transformations. DMSO (see Recipes)


  1. Microcentrifuge


  1. Inoculate overnight culture at room temperature (RT) in 5 ml SOB or 2x YT.
  2. Add overnight to 500 ml of SOB or 2x YT in 4 L flask to maximize aeration. 
  3. Add 36 ml of 5 M NaCl. Shake well at 30 °C.
  4. Grow to OD600 of 0.5. About 3 h.
  5. Spin cells. Drain pellet very well. Suck out extra liquid.
  6. Gently resuspend in 50 ml of cold TFB. Incubate for 15 min on ice.
  7. Prepare a dry ice/ethanol bath (should be thick in consistency) or liquid nitrogen.
  8. While swirling cells add 1.75 ml DMSO (no need to sterilize DMSO).
  9. Incubate cells for 10 min on ice and chill eppendorfs on ice.
  10. Add 0.5 ml cells to each Eppendorf and quickly drop tubes into dry ice bath. Store cells at -70 °C for up to 12 months.
  11. Use 100 μl for transformation. Heat shock at 42 °C for 1.5 to 2 min.


  1. SOB or 2x YT (1 L)
    Tryptone             20 g
    Yeast extract       5 g
    5 M NaCl             2 ml
    pH to 7.0 and bring up to 1 L
    Autoclave and add 2.5 ml 1 M KCl, 10 ml of 1 M MgCl2, 10 ml 1 M MgSO4
  2. MES
    1 M MES solution made to pH 6.2 with KOH
    Filter sterilized and stored frozen
  3. TFB (50 ml) enough for 80 tubes/400 transformations
    0.5 ml of 1 M MES
    0.6 g of RbCl (makes 100 mM final conc.)
    0.45 g MnCl2 (45 mM)
    0.077 g CaCl2.2H2O (10 mM)
    0.04 g hexamine cobalt chloride (3 mM)
    Store at 4 °C
    Keeps for several months
    Use it cold


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Copyright: © 2011 The Authors; exclusive licensee Bio-protocol LLC.
How to cite: Li, X. (2011). RbCl Super Competent Cells. Bio-101: e76. DOI: 10.21769/BioProtoc.76.

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Issiaka Bagayoko
university (UCLouvain)
In the procedure, step 11, why incubation should be between 1.5 to 2 min and not at 45 seconds
3/29/2019 3:56:25 AM Reply
Steven Cummings
Ohio State University

I tried to follow the link in your references section but could not get it to work. Do you by any chance have a different link?

Thanks a lot!
12/6/2014 4:39:08 AM Reply
Xiyan Li
Department of Genetics, Stanford University, USA

Sorry, I don't have it.
You may ask the PI if you really want an original copy.

12/6/2014 7:47:04 AM

Hongjiu Dai
when we prepare some vectors, some fragments have toxin genes and sequences. My may be hard to get vector amplification in E.coli. Do you think your super competent cells could solve this problem, thanks
5/27/2014 2:26:50 AM Reply
Xiyan Li
Department of Genetics, Stanford University, USA

No, i won't help.

What you need is a suitable host strain that us more tolerant.

I would also try low copy number plasmid and low culture temperature, e.g. 30C or even 25C.

5/27/2014 8:11:00 AM

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