Anywhere between 10-25% should be more than enough. Also, make sure your cultures are compatible with the storage method. Not all cultures will do well long term on frozen glycerol storage.
For bacterial culture stock you have to use 25-30% glycerol stock. Bacteria producing spores are ok to keep in 20% glycerol stock (eg. Bacillus). But Burkholderia does not produce spore. So try to keep them in 25-30% glycerol stock solution. One more thing you can do. Make bacterial culture on NB/TSB/LB or other good bacterial media and then transfer 30/40 ml solution to small small glass tube and keep them in 4 degree Celsius temp.
I am agree with all previous researchers. Glycerol stock ranges from 15-30 %. Its depends on the type of Bacteria. Use can also refer the MBM series "Cryopreservation Techniques".
Depends on the species. I normally use 15-20% for E. coli with no problems and have used DMSO in the past. However in some species (e.g. clostridia) we see dramatic decreases in viability with increasing glycerol concentration (15% was an order of magnitude better than 20% and 10% was an order of magnitude better again!). In our tests 10% gave the best viability but produces very hard ice - similar to DMSO. As a compromise we use 12% - good viability and easier to scrape some off to streak.
I used 30%. My sincere thanks to Rupesh Divate, Ana Lucia Cordova, Naryan Chandra Pal, Kaushik Bhatta Charje, Ami Patel, Sudheer Babu, Andres Gon Zalez-Rodriguez, Igor Brown, Robert Gagan for your Valuable suggestion.
Every bacterial specie could have little differences. I use 20% commonly and it works fine. I used centrifuge 5-10 ml of bacterial culture. After that, I add 1ml of fresh medium with 20% glicerol to the pellet. If you freeze it quickly (with liquid nitrogen, for example) it would be better.