I want to create concentrated bacterial cells by centrifuging my overnight culture and washing them to make bacterial pellets. Then I need to store my pellets before submitting them for DNA extraction and whole genome sequencing. My question is, how should I store bacterial pellets? Can I just place them in the freezer for a week before they're picked up for extraction or do I need a reagent like glycerol or DSMO to keep them viable? Thank you.
Aaron Reyes , I usually centrifuge my bacterial cultures samples like you, get rid of all supernatant and stored the pellets in -20 C. These are usually fine for 1-2 weeks. However, if storing for longer periods, I store the pellets in -80 C.
The pellets can be stored in -20°C for about 2 weeks and -80°C for about 1 month.
Using glycerol is better for long time storage in -80°C
Bacterial glycerol stores are essential for long-term plasmid preservation. Although plasmid DNA can be stored at -20°C, several laboratories make bacterial glycerol stocks of their plasmids. When you need extra plasmid DNA, the plasmid will already be in your selected bacterial strain, so you won't have to collect more competent cells and retransform.
Bacteria on an LB agar plate can be kept for several weeks at 4°C. If you wish to keep bacteria for a longer period of time, you'll need to create glycerol stocks. The inclusion of glycerol stabilises the frozen bacteria, preventing cell membrane damage and maintaining cell viability. Bacterial glycerol stocks can be preserved for many years at -80°C.
Actually, I would recommend a combination of deep freezing and glycerol. Freezing at a temperature of -80°C could help preserve your bacterial cells for years, while glycerol will help prevent the formation of ice crystals during freezing.
Freezing at -20C should be fine over the short term. I would use -80 C if available just to be sure. Glycerol stocks are needed only if you wish to grow the strains again.
As many said above for DNA extraction you do not need glycerol but first snap freeze the pellets in liquid nitrogen and then store at -80C until sent for DNA extraction (transport in dry ice).
Good luck
Shajahan
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