IGEM:Paris Bettencourt 2012/Protocols/Competent Cells With CaCl2

Protocol: [math]\displaystyle{ CaCl_{2} }[/math] Competent Cells

This protocol makes 4 ml of competent cells, and can be easily scaled up to make more. The cells are typically stored in 110 ul aliquots, so this will make about 35 tubes. A typical transformation uses 20 ul of cells.

NOTE: Never vortex competent cells. Resuspend by pipetting with large Pasteur pipettes.

The night before  :

1. The night before, inoculate a 5 ml culture and grow overnight with selection.

The day of  :

1. Dilute cells ~ 1:200 into selective media.
   • For this example add 250 ul to 50 ml of selective media.
   • NOTE: The protocol is easily scaled to increase the number of cells.
2. Grow the cells to an Optical Density (OD, 600 nm) of 0.6 – 0.7.
   • Use a large flask, 500 ml, for good aeration.
   • Use a baffled flask for fastest growth.
   • This takes about 3 hours depending on the cells.
   • Medium-heavy cloudiness by eye is fine.
3. Spin down the cells at 4 ºC, 4000 rpm, 15 minutes.
   NOTE: Keep the cells at 4 ºC from now on.
4. Resuspend cells in 15 ml, ice-cold 100 mM CaCl2.
   • Leave on ice 4 hours to overnight.
5. Spin down the cells at 4 ºC, 4000 rpm, 15 minutes.
6. Resuspend cells in 4 ml, ice-cold 100 mM CaCl2 + 15% glycerol.
7. Aliquot into pre-chilled Eppendorf tubes. Use immediately or store at -80ºC.

NOTE: Frozen cells are only good once. Do not refreeze cells once thawed.

Solution Recipe

Material	Amount	Notes
LB with antibiotics	50 ml	-
100 mM [math]\displaystyle{ CaCl_{2} }[/math]	15 ml	Ice cold
100 mM [math]\displaystyle{ CaCl_{2} }[/math] + 15% Glycerol	4 ml	Ice cold