Submitted to: Biotechniques
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/1996
Publication Date: N/A
Interpretive Summary: Culturing microorganisms, in the absence of oxygen, often requires that accumulating gases be vented during growth. Preventing the release of such by-products usually causes inhibition of the organism and this can then lead to a decreased yield of fermentation products such as organic acids and ethanol. It is common to release pressure with a needle placed through a septum covering the fermentation vessel. Unfortunately, this design will only keep the system free of oxygen if the fermentative gases are being produced rapidly enough to result in a positive displacement of air within the fermentor. Thus, the system may come in contact with oxygen through the vent during the initial and late stages of the fermentation when production of gases is low. One-way valves can be used for this purpose, but they are typically quite expensive for routine growth involving numerous culture tubes or flasks. We present a very simple and rapid method to construct an inexpensive, autoclavable one-way valve using a 1 cc syringe and a few miscellaneous items that can be found in most laboratories.
Technical Abstract: We present a very simple and rapid method to construct an inexpensive, autoclavable one-way valve using a 1 cc syringe and a few miscellaneous items that can be found in most laboratories. First, the plunger is removed from a 1 ml syringe. The rubber nub is pulled off the plunger and cut in half as shown in the diagram, with either scissors or a razor blade. The very tip portion is discarded and the remaining half of the rubber nub is reinserted back into the syringe in the same orientation as before. A 4 mm glass bead creates the valve by seating against the fabricated rubber washer in the syringe. To keep the bead snugly against the opening, a spring is inserted. Small springs may be purchased from most hardware stores, but we have found that those used in disposable pens work excellent. If desired, a small amount of glass wool can be added at this point to prevent contamination from entering through the valve. Finally, the apparatus is completed by reinserting the plunger back into the syringe until only a slight amount of pressure is against the spring. Seal it into place by poking a needle heated with a Bunsen burner through the syringe and into the plunger at the location shown by the arrows. This will melt the plastic and essentially "weld" the plunger in place. The valve may be made more compact by cutting the top portion of the syringe and plunger off using wire cutters.