Preparation of plates for bacteria:

LB/Amp plates

  1. Dissolve 25 grams of LB mix in approximately 800 ml of water.  Bring the final volume to 1 liter.  Pour this into a 2 liter flask and add 15 grams of Bactoagar (not agarose).  Cover top with foil and autoclave for 20 minutes.
  2. After autoclaving, vigorously swirl the solution in the flask to mix molten agar.  Cool the solution to 50 oC - this is when you can stand to hold the bottom of the flask for 10 to 20 seconds.
  3. Add 100 mg of Ampicillin and swirl until it dissolves.
  4. Commandeer a space that will hold 40 plates, unstacked.  Pour plates to a depth of approximately 3mm. If there are bubbles on the surface of the agar, these can be remove by briefly flaming the surface with a bunsen burner.
  5. Leave the plates out at room temperature and unstaked.  Wait at least a few hours before stacking the plates and wait at least 24 hours before putting the plates in th refrigerator.  LABEL THE PLATES WITH THE DATE AND NOTE THE PRESENCE OF AMP.
  6. Store plates in the plastic sleeve in a refrigerator.
Option for turning LB plates into LB-Amp plates
Add 200 ul of a 5 mg/ml stock of ampicillin; add drops of ampicillin in several locations on the plate so that it is uniformly distributed. Spread the solution around on the plate with a sterile glass rod and then allow it to absorb into the plate. A stock of 25 or 50 mg/ml ampicillin is in the -20 oC freezer, dilute the required amount to 5 mg/ml with water.

Use of X-gal for blue/white screening.

  1. Spread a mixture of 40 ul of 2% X-gal and 60 ul of water onto a plate, let this diffuse into the plate for at least 1 hour
  2. Just before plating the transformed cells, add 10 ul of 100 mM IPTG to the cell mix.
  3. In general, transformants that are white contain an insert in many of the standard cloning vectors.  If you are working with one of our plasmids that has a ß-galactosidase reporter gene, you may find it useful to use blue/white screeing to identify plasmids that contain the reporter.  Usually, a low level of activity is detected, presumably because the reporter is transcribed in bacteria.