Creating a Glycerol Stock of your Addgene Plasmid
Bacterial glycerol stocks are important for long-term storage of plasmids. Although you can store your plasmid DNA at -20°C, many labs also create bacterial glycerol stocks of their plasmids. This way, when you want to make more plasmid DNA, the plasmid will already be in your desired bacterial strain and you will not need to obtain more competent cells and retransform.
Bacteria on an LB agar plate can be stored at 4°C for a few weeks. However, if you want to store bacteria for a longer time, you will need to establish glycerol stocks. The addition of glycerol stabilizes the frozen bacteria, preventing damage to the cell membranes and keeping the cells alive. A glycerol stock of bacteria can be stored stably at -80°C for many years.
Follow the steps for Inoculating an Overnight Liquid Culture.
After you have bacterial growth, add 500 µL of the overnight culture to 500µL of 50% glycerol in a 2 mL screw top tube or cryovial and gently mix.
Freeze the glycerol stock tube at -80°C. The stock is now stable for years, as long as it is kept at -80°C. Subsequent freeze and thaw cycles reduce shelf life.
To recover bacteria from your glycerol stock, open the tube and use a sterile loop, toothpick or pipette tip to scrape some of the frozen bacteria off of the top. Do not let the glycerol stock thaw! Streak the bacteria onto an LB agar plate containing the appropriate antibiotic.
Grow your bacteria overnight at the appropriate temperature (growth conditions, including copy number and growth temperature, can be found on your plasmid's information page) to isolate individual bacterial colonies ready for inoculating plasmid prep cultures.
Note: Make the 50% glycerol solution by diluting 100% glycerol in dH2O.
Note: Snap top tubes are not recommended as they can open unexpectedly at -80°C.
Tips and FAQ
How much glycerol should I use?
The optimal concentration of long-term glycerol storage is unknown. Most labs store bacteria in 15-25% glycerol. Addgene stores all of our bacteria in 25% glycerol stocks.
Do I need to make a separate overnight liquid culture for minipreps?
No! Save time and prepare the glycerol stock at the same time you are isolating your plasmid DNA. In the morning, when you retrieve your liquid bacterial culture, take 500µL of culture to make your glycerol stock before you begin your miniprep.
How stable is my glycerol stock?
Try not to freeze/thaw your glycerol stock too many times. At Addgene, when we want to grow more of a plasmid, we place the glycerol stock on dry ice while streaking onto LB agar so that it never thaws. We resequence our stock after every 100 uses.