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From 2010.igem.org

Making competent cells

Materials:

- bacterial culture

- centrifuge

- 0.1 M MgCl2

- 0.1 M CaCl2

- 80% glycerol

Protocol:

1. Cultivate 100 mL LB medium, 37 °C o/n with shaking(140 rpm)

2. Cultivate 50 mL further in 800 mL LB, ~ 2 hours at 37 °C with shaking (140 rpm) until OD601 = 0.4

3. Centrifuge 4500 rpm, 6 min, 4 °C

4. Resuspend pellet in 80 mL ice-cold 0.1 M MgCl2

5. Centrifuge 4500 rpm, 6 min, 4 °C

6. Resuspend pellet in 50 mL ice-cold 0.1 M CaCl2 (do not vortex, stir with Pasteur pipet, solution should look like milk)

7. Incubate 15 min on ice

8. Centrifuge 4500 rpm, 6 min, 4 °C

9. Resuspend pellet in 40 mL 0.1 M CaCl2 (do not vortex, stir with Pasteur pipet)

10. Incubate 60 min on ice

11. Centrifuge 4500 rpm 10 min 4 °C

12. Add ~1 à 2 mL (depends on the amount of pellet) ice-cold 80% glycerol

13. Divide in parties of 30 µL and quickly put them in the liquid nitrogen

14. Freeze in -80 °C