This method was developed at Bloomington to support high-throughput media preparation. Trays of fresh vials are sealed with Glad® Press’n Seal® plastic wrap instead of plugs. This material is easy to handle, quick to apply, and relatively inexpensive. Vials sealed in this way stay moist much longer than plugged vials.
Glassware is racked by hand in cardboard trays with dividers that hold 100 vials in a 10 x 10 array. 80 trays can be racked in ~2.5 hours (this step can be eliminated by using pre-racked plastic vials).
Trays of vials are filled with medium using the Droso-Filler™ media filler (Genesee Scientific #59-168) and a heavy duty peristaltic pump (Watson-Marlow 620DiN) to keep the filler filled. Uniform delivery from the filler requires that the food be uniformly hot and at a consistent volume, so a pump powerful enough to quickly deliver a liter of food is very helpful. This allows a tray to be filled, covered with cheesecloth and placed on the cooling rack every 25 seconds or so. The pump can be stopped with a foot peddle if a variable pause is needed, but the filler can’t be left for long because delivery becomes uneven as the food cools. 80 liters of food can be dispensed into vials (~10 ml per vial) in less than 45 minutes.
Trays are left to cool for at least 2 hours. Condensation is slow to evaporate with this method so if the vials are sealed while they are too warm, they will be wet. When the food is cool, each tray of vials is covered with a sheet of Press’n Seal®. A piece long enough to cover the vials is torn off, laid on top of the vials tacky-side down, and briefly rubbed with the flat of the hand to seal the plastic to the tops of the vials. Another cardboard tray (without the dividers) is then inverted onto the sealed vials and the entire ensemble is then inverted so that the vials are now upside-down. This makes a better seal between the vial and the film. It takes a little over an hour to seal, date and stack 80 trays of vials, compared to 8 to 10 hours to plug with rayon.
We store trays (still upside-down) at 12 degrees C. If you store them at room temperature, we recommend putting trays into sealed plastic bags.
A drawback of this method is that any small gaps in the seal can allow flies to enter. If trays are stored at room temperature, we recommend putting the trays into sealed plastic bags.
We keep trays inverted for use so we don’t have to peel the film away, we just pull off one vial at a time (the cardboard grid holds the array in place). We put trays into sealed plastic bags when unattended.
Alternatively, you can flip the tray so the vials are rightside-up and slice the wrap between rows with a razor blade before use so that the film can be peeled from one or two vials at a time without disturbing the seal on the rest. If you use this method, do check for gaps or wrinkles and correct the seal as needed and, again, we recommend putting unattended trays into sealed plastic bags.
Alternatively, you can turn the tray rightside-up, pull off the film and plug the vials prior to use.