A. Small Scale Cultures
Experiments using E. coli cells should always be done on fresh cultures, either from a freshly streaked plate or from a glycerol stock. To grow a small scale E. coli culture, prepare 3-5 ml of LB (or appropriate broth - include antibiotic if the culture contains a plasmid) in two sterile 50 ml tubes. (Note: smaller tubes can be used but the culture will not be appropriately aerated and hence will not grow well and is not recommended). Inoculate one tube with a single colony from a fresh plate or a scraping from a glycerol stock. The second tube is used as a broth control. Incubate both tubes at 37 deg C, shaking vigorously overnight. Inspect the tubes the next morning. The broth control should be clear and the inoculated culture should be very turbid. Make a note of any debris found in the tubes and only incubate longer if the culture is not dense. Do not allow cells to overgrow. Use immediately. For some applications, cells can be stored at 4 deg C for short periods prior to use.
B. Permanent Storage
For every culture used, in particular, for newly constructed strains or for cells containing plasmids, a permanent glycerol stock must be prepared as soon as the construct has been confirmed and this stock must be placed in the laboratory stock collection with the appropriate documentation and location information. Failure to follow these procedures will result in serious penalties. This procedure pertains not only to E. coli but to any organism for which a deep freeze stock can be prepared. Also, all plasmid constructs, including construction intermediates, must be maintained in cells, not as naked DNA stocks. For each construct, at least 2 stocks should be made. To prepare a glycerol stock for E. coli cells, combine 1.4 ml of a freshly grown overnight culture with 0.6 ml of sterile 50% glycerol. Mix well. Transfer to two freezer vials labeled with the strain name, the date and your initials (not an eppendorf tube). Immediately place into a dry ice/ethanol bath or into a box in the -80 deg C freezer. Note the location and enter data into the strain book.
