Glycerol stocking is used when bacteria is wanted to be stored for use at a future date. Bacteria can stay frozen for years, and it is still possible to be alive once they thaw.
Why do we need glycerol stock?
When we hear the word bacteria, we often think of the dirty germs around us. But not all bacteria are harmful. Scientists use bacteria to help develop beneficial things, such as antibiotics.
Sometimes scientists find cool and interesting bacteria they want to save for later. If they leave their bacteria in the fridge, they may only be able to survive a few weeks. They also run the risk of mutating or getting contaminated.
How long can bacteria survive using this technique?
The survival rate of bacteria that have gone through glycerol stocking is indefinite. It all depends on the bacteria. Too much glycerol can cause stress on the bacteria, killing it. Some bacteria are better at withstanding frozen life than others.
How to glycerol stock
In a lab, researchers will take some bacteria that have been grown on an agar plate, and mix them in a vial with a broth. A commonly used example of an agar plate is LB agar, which is a rich medium that is used to grow and multiply bacteria.
Glycerol can help stabilize the bacteria by protecting the cell membranes from damage. Therefore, a glycerol solution is then added to the vial as well. Afterward, the vial is vortexed, which is rapid mixing, to fully combine the contents of the vial.
The vial is now going to be stored in a freezer that is set at -80°C. That's colder than any freezer you have in your house; most of them are set at around -17.8°C.
All procedures might not look the same despite having the same end goal. Here is a video showing the process of glycerol stocking: Creating Bacterial Glycerol Stocks
Let's see if your frozen bacteria is still alive!
We can do this by observing if they can still grow and multiply. After keeping the bacteria in the freezer for a chosen amount of time, take them out. If you would still like to store them after testing, make sure they stay on ice and you work quickly.
A bit of bacteria is taken on a sterile loop and then inoculated on an agar plate. Inoculating is easy! Take the loop with bacteria and run it gently along the agar in any pattern you like!
Quickly place the frozen bacteria back into the freezer and place the agar plate into the incubator at 26°C for 24-48 hours.
Once the plates are out of the incubator, you can observe whether or not your bacteria were able to reproduce. If they did and there is growth on the plate where you inoculated...
CONGRATULATIONS! You just froze and thawed life!
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