Creating Competent E. coli Cells

Goal

• Goal: To create competent E. coli cells using either of the two methods listed below.

Pre-Protocol Questions

1. Do you know how to triple-streak cells onto a plate?
2. Do you have the necessary media plates (LB, Tryptic Soy, etc.)?
3. Do you know how to use the huge ultra-centrifuge in Superlab?

Current Version: CaCl2 Competent Cells without Sodium Ions (from Bash)

Special Reagents Needed

• TF1 Solution — Add in this order

1. 28.1 mL 80% glycerol
2. 7.5 mL 1M MnCl2 in acidified water (83.3ul concentrated HCl added to 5ml water; add 1.26g MnCl2 and dissolve; add water up to 10ml. If the solution has a brown-orange precipitate, then MnCl2 oxidized and a new solution is needed)
3. 4.5mL 1M Potassium Acetate
4. 15mL 1M KCl
5. 3 mL 0.5M CaCl2
6. Fill to 150 mL and adjust pH to 5.8 with 0.2M acetic acid (or 0.2M KOH). Go very slow with this step; if the solution goes above 7.0, then the MnCl2 will precipitate and will not go back into solution.
7. Filter sterilize only. Place in 3rd floor cold room.

• TF2 solution. Place in the 3rd floor cold room.

1. 200 ul 1M MOPS, pH 6.5
2. 200ul mL 1M KCl
3. 3 mL 0.5M CaCl2
4. 3.75 mL 80% glycerol
5. Fill to 20mL with water and adjust pH to 6.5 with 0.2M acetic acid or KOH
6. Filter sterilize only. Place in 3rd floor cold room.

• Growth media (Either for 800ml of cells, or double the number of flasks. There will be enough TF1 and TF2 for this double volume.)

1. Fill a graduated cylinder to ~700ml with MilliQ water
2. Add 4g Yeast Extract
3. Add 16g Bactotryptone
4. Add 4g MgSO4
5. Dissolve and fill up to 800ml with water
6. Adjust to pH 7.6 with 1M KOH (not NaOH)
7. Put 400ml in each of two 2L flasks and immediately autoclave.

Day 1

1. Triple-streak previous competent cells for single colonies. Use a Tryptic Soy plate or an LB plate with antibiotics, if applicable.
2. Create TF1 solution
3. Create TF2 solution
4. Create Growth media
5. Create p1000 tips with 0.25cm cut off sterilely. Place in the 3rd floor cold room.
6. Sterilized large ultra-centrifuge tubes. Place in the 3rd floor cold room.
7. Place two 50ml Falcon tubes in the 3rd floor cold room.

Day 2

1. From this grown plate, pick a single colony and inoculate 10ml LB (+ antibiotics if applicable) in a 50ml Erlenmeyer flask. Grown overnight at 37 degrees with shaking.

Day 3

Important: Treat cells gently after addition of TF1 Solution — no vortexing or vigorous pipetting — as this will greatly reduce the competency.

1. Inoculate both 400ml LB flasks with 4.5ml of overnight growth and shake at 37 degrees. Use 2ml if you are using four 400ml LB flasks.
2. Turn on the Superlab ultra-centrifuge, and chill to 4 degrees.
3. Turn on Superlab swinging rotor centrifuge, and chill to 4 degrees.
4. Measure OD after 1 hour and then every 30 minutes, until O.D. at 600nm is 0.2-0.4 (~3 hours). Using a 13mm tube, this translates to Ab 0.25-0.52.
5. Place flasks on ice, or even better, in an ice bath. Take to Superlab.
6. Put cells into four total large ultra-centrifuge tubes, and balance to 0.1g. This will be ~200ml each. (Use six ultra-centrifuge tubes, each with ~266ml, if you are using four 400ml LB flasks.)
7. Pellet cells for 20 minutes at 3700 rpm / 3200 x g at 4 degrees in Superlab ultra-centrifuge.
8. Decant (gently pour off) supernatant and gently resuspend cells in 20ml ice cold TF1 solution per ultra-centrifuge tube by pipetting up and down with a serological pipette. Keep on ice.
9. Consolidate cells to two 50ml Falcon tubes and chill on ice for 20 minutes. Balance to 0.1g. (Use three 50ml Falcon tubes if you are using four 400ml LB flasks.)
10. Pellet cells for 20 minutes at 3700 rpm at 4 degrees in the swinging rotor centrifuge.
11. Decant supernatant and gently resuspend cells in 2ml ice cold TF2 solution per pellet by pipetting up and down with a cut-off p1000 pipette tip. Chill on ice for 10 minutes. Consolidate into one tube.
12. In cold room, aliquot 50 ul into the 0.6ml tubes, using the cut-off p1000 tips and the electronic pipettor.
13. Flash freeze aliquots in liquid nitrogen.