Freezing Strains

Supplies

1. Overnight liquid culture
   Several milliliters of overnight liquid culture grown in a suitable medium for each sample to be frozen.
2. 80% Glycerol or DMSO solution
   A standard lab solution. Grab your own stock bottle and keep it in your workspace.
3. Sterile 2 ml cryovials and circular cap inserts
   Found on a shelf above the colony counters in 1.436. Take a bag for yourself and keep it in your workspace, closing it with an alligator clip when not in use.
4. Cryotag rectangular 1.28" x 0.50" labels
   Found in the bottom drawer of the office supply cabinet below the message board in 1.436.
5. Clear tape
   Found in dispensers throughout lab or on the office supply cabinet in 1.436. Do NOT use "magic" tape (which is translucent and does not stick as well at –80°C). Use fully clear tape.
6. Freezer box

Labeling Tubes

1. Sample naming – Every strain has a three letter designation (usually the initials of someone) and a strain number. When freezing new samples, either append them to your own strain series or obtain the next available numbers from a standard series (e.g. JEB) by looking in the Strain Database.
2. Write the three letter designation, the strain number, and the date (MM–DD–YY) on a CRYOTAG label for each sample. Also include whatever other distinctive information about the strain that can be fit onto the label (e.g. experiment, population, time).
3. Stick the label on tube horizontally, and completely cover it with one strip of clear tape for longevity.
4. Write the strain number on the plastic circular cap insert, so that it will be visible from above when looking down on the tube in a freezer box.

Freezing Samples

You will need to add a cryoprotectant to your sample of cells to be frozen. Generally this is 80% glycerol, though for some experiments DMSO is used instead. The standard amount to add of this cryoprotectant is one-fifth the volume of your cells. This gives a final concentration of 13.3% glycerol or 16.7% DMSO.

If you are using DMSO, wear gloves and avoid contact with your skin!

For most samples, you can follow this procedure:

1 Add 200uL of 80% glycerol to each empty cryovial. Glycerol is extremely viscous. Use the 1 ml pipettor because the tips have a larger aperture. Be careful to pull liquid into the pipette tip slowly and to let excess liquid drip off the outside before you remove the tip from the stock bottle. Use the repeat pipettor if you are freezing >12 samples.

1. Add 1000uL of each revived strain to the appropriately labeled cryovial using a 1 ml pipettor.
2. Vortex each cryovial at high speed to be sure that these solutions are uniformly mixed.
3. Place the tubes in the next positions available in your boxes or the main lab stock boxes. Record the box, rack, and freezer names and numbers.

Updating the Strain Database

It is very important to immediately add information about the samples you have archived to the lab database so that they can be located by others and posterity. You should also keep a record in your lab notebook of where these samples came from. Instructions for how to use the strain database are located here:

Strain Database Instructions

Label Templates