Fridge & Freezers

What are they and why do we use them? What types are there?

Fridges and freezers are used to keep reagents cold. Any lab requires at least a 4°C Fridge and a -20°C Freezer, but to be truly efficient you will also need to find a -80°C Freezer to store glycerol stocks and chemically competent cells.

4°C Fridge - Any old bar fridge will do. I stole my sister’s one from college and it worked fine. This is simply for keeping cultures and buffers (such as P1 Resuspension Buffer) cool. If you have more than one person working in your lab, you’ll likely need to upgrade to a full sized fridge, since everyone accumulates various reagents that should be kept in the fridge…but a cheap one will still suffice.

-20°C Freezer - Most biotech reagents are some form of thermosensitive, somewhere between quite thermosensitive > EXTREMELY THERMOSENSITIVE. As such, you need a very specific kind of freezer - one without a defrost cycle. This can generally be confirmed by the large build up of ice, but that doesn’t guarantee that a fridge isn’t entering a defrost cycle every now and again. Reagents such as T4 DNA ligase buffer will not survive more than one defrost cycle, so it is critical that you know your freezer won’t ruin your enzymes.

-80°C Freezer - These enormous beasts cost an arm and a leg to run and often require a special high-amp power socket to power. It may be financially unfeasible to invest in one of these as a solo researcher, which is why it is highly recommended to find a shared lab space for synthetic biology. These freezers keep glycerol stocks and competent cells stable for longer than a decade. Without one of these you will likely need to constantly remake your competent cells.

When do you use?

The fridges and freezers never stop running. Most things (DNA, Enzymes, antibiotic stocks) are stored in the -20 freezer. Things that are alive, such as cells on a plate, go in the fridge. Freezing E. coli cells will lyse their membranes, killing them.
The -80 is technically for long term stable storage, but DNA frozen at -20 is honestly as stable as glycerol stocks at -80. The main advantage of the -80 is always having a stable line of competent cells on hand.

How do you use?

5 second rule! Have your ice bucket with ice ready and submerge any tube (deep enough in the ice that the liquid is surrounded, but not so deep that ice could melt near the lid) immediately after removal from the freezer. Remove enzymes one at a time and do not hand thaw! If it is still liquid, it’s in glycerol and definitely should not be hand-thawed. This is especially true for T4 DNA ligase buffer.

Restriction enzyme buffers, DNA ladders, purified DNA and plasmid DNA can all be hand-thawed. If a precipitate forms in a buffer, briefly vortex it to redissolve.

Competent cells and glycerol stocks removed from the -80°C Freezer can be hand-thawed, but be careful of freezer burn. Let the outside of the tube warm up closer to room temperature before gripping it tightly.