Team:UCL London/CaCl2


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CaCl2 Competent Bacteria - Generating and Transforming


Before Starting;

Pour minimal media plates. 5x M9 salts etc overleaf. Prepare 100ml LB per strain. Prepare 50ml ice cold 0.1M CaCl2 / 15% glycerol per strain Pre-chill eppendorf tubes

Day 1

1 Streak cells on minimal agar plate. Incubate 37C overnight.

Day 2

2 Pick a colony into 5ml LB + 100µl 1M MgSO4 Incubate 37C in shaker overnight.

Day 3

3 Inoculate 100ml LB in pre-warmed conical with 1ml of the 5ml O/N culture from Day 2.

4 Incubate 2hrs in 37C shaker until the cells at early log phase of growth curve (A600 ~ 0.3)

5 Transfer to chilled, sterile 50ml Falcon tube and incubate on ice 10min

6 Cf 3300g 5min in benchtop RmT. Cf.

7 Resus in 10ml ice cold 0.1M CaCl2 / 15% glycerol and incubate on ice 30min

8 Cf 3300g 5min in benchtop RmT. Cf.

9 Resus in 1ml ice cold 0.1M CaCl2 / 15% glycerol.

Transfer 100µl aliquots to pre-chilled, pre-labelled eppendorf tubes. Store -70C.


  5x M9 salts in 500ml dH20.
  Na2HPO4	32g
  KH2PO4	7.5g
  NaCl         1.25g
  NH4Cl	2.5g

Minimal media plates for competence

In 50 ml Falcon;

39ml melted Bacteriological Agar solution (=50C) 10ml 5x M9 salt solution 1ml 20% (w/v) D-glucose 50µl 2mg ml-1 thiamine 5µl 1M CaCl2 100µl 1M MgSO4

0.1M CaCl2 / 15% glycerol

In 50 ml Falcon;

5ml 1M CaCl2 7.5ml 100% glycerol


Before Starting

Prepare 5ml LB per strain. Prepare appropriately selective nutrient agar plates


Day 1

1 Add 1-5 µg of ice cold DNA to 100 µl of competent cells on ice. Incubating for 45 min.

2 Heat shock cells by placing tubes in 37C water bath for 10min.

3 Place cells on ice 2 min

4 Add cells to 5ml LB (in 15ml or 50ml tube). Shake for 1 hour at 37C.

5 Plate at least 100µl onto selective nutrient agar plates.

Day 2

6 Pick a colony into 2ml selective LB. Incubate 37C in shaker overnight.

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