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Image of bacteria for article on colony picking after transformation.
Published On: July 5th, 2022

Bacterial transformation can also be performed using electroporation, but this method is less common. It runs on the same principle as heat shock protocol, but electricity is used instead of heating the bacteria. Electroporation sometimes results in more transformed colonies, but not always.Once transformation has occurred, it’s time to pick colonies after transformation. Colony picking protocol isn’t too difficult but is quite an important process of bacterial transformation. Read on to learn about the precise protocol when picking colonies.

Description of Picking Colonies After Transformation

Once transformation is complete, you will be picking colonies from agar plates.
You should have three bacterial plates to choose from:

  • The ligation plate.
  • A plate with no fragment but with lipase (control plate).
  • A plate with no fragment or lipase.

The ligation plate will have myriad colonies, and the other plates will have less. It’s important to note that when you pick colonies after transformation, it is chosen by the ratio of colonies you have on your control plate (the one with lipase) to the number of colonies on your ligation plate.

Here is an example if you are performing standard sticky-ended directional cloning.If you have ten times more colonies on the ligation plate compared to the control plate, 9 out of 10 colonies should likely have the correct fragment ligated into it.

However, there are bumps in the road sometimes when picking colonies after transformation, such as multimers or concatemers. Because of this, you’d likely pick five to ten colonies, depending on outside factors.

In contrast, if you only have two times more colonies on the ligation plate than the control plate, you would pick ten colonies or more. You can always place plates back in the refrigerator and redo the process. Unless your ligation is very complex, you wouldn’t pick a large number of colonies, such as 50. It will just slow you down.
When picking colonies after transformation, an enzyme fails to work in some cases. This can result in no difference between the ligation and control plates. If this happens, you’ll have to start the entire process over. Some tips to prevent this from happening include:

  • Decreasing the background
  • Digesting for longer
  • Exposing to less UV
  • Using someone else’s enzymes
  • Dephosphorylating for longer

There is a certain protocol when it comes to the act of picking colonies after transformation using an automated colony picker or performing the process manually.

What Is the Protocol for Picking Colonies After Transformation?

The protocol for picking colonies after transformation must be performed in a sterile environment, typically with a Bunsen burner or class 1 hood nearby. It is very important not to cross-contaminate. The protocol is:

  • Take the plates out of the incubator (which should be 37°C), upside down. This is the same way you have put them in. Place them on the benchtop.
  • Have a pipettor handy. You must pipette 3 to 5 mL of LB media (catalog numbers L3522, L2542, or L3022), with the correct concentration of antibiotic into 25 to 60 mL tubes. The amount of air is also important. There should never be more than a 1:3 ratio of liquid to air. Ideally, the ratio should be much higher.
  • Next, place a sterile pipette tip on another pipette with one hand. Using your other hand, pick up the upside-down ligation plate.
  • Turn the plate over, and touch the sterile pipette tip to a bacterial colony that is away from other growth.
  • Place the pipette tip with the bacteria on it into one of the LB tubes. Gently move the tip so that the bacteria is released into the liquid.
  • Once all of these steps are complete, you must culture the tubes overnight in an incubated orbital shaker, which should be 37°C and 190 to 225 rpm.

You can also freeze colonies during the process of picking colonies after transformation. Colonies in liquid can be viable at 4°C for several weeks.

Hudson Robotics has been the leading supplier of automated products for over 38 years. To learn more about picking colonies after transformation, speak to a representative today!