I have three tubes of 5 mL each of starter culture of overnight grown bacteria with three different plasmids stored at 4 degrees. I was curious if these cultures can be used to prepare glycerol stocks?
Ya, you can use the culture stored at 4 degrees to prepare glycerol stocks, provided it is not stored at 4 degrees more than 2days because bacteria are known to throw plasmids while long storage and repetitive culturing. Another thing do not prepare glycerol stocks directly from a culture stored at 4 degrees, better you revive cells at 37 degrees for 4 to 5 hrs and prepare glycerol stocks.
Ashish has already answered your question but I have faced few problems with themophiles so if you are working with thermophiles its always better to preserve them without any cold shock. Thank you.