Low-Cost Fermentor Andrew S. ~ o ~ k i n s ' Alverno College, P. 0.Box 343922, Milwaukee, WI 53234
Laboratory experiences in molecular biotechnology techniques such as agarose gel electrophoresis and expcrlments with plasmids need substantial quantities of DNA's when a number of students are involved. Punfied DNA is used in demonstrations of techniques, as size markers for gels and for restriction analysis and cloning experiments. These DNA's can be purchased at high cost, but they also can be isolated and purified in the laboratory as part of an undergraduate project. This article describes some simple ways to do this at minimal cost. Traditionally, volumes from 500-1000 mL of bacterial culture are grown in large flasks agitated in a water bath, but this can be a messy and clumsy approach. The growing cells rarely exceed a density of 2 x lo9cells/mL. Commercial fermentors, or bioreactors, as they are called, are available in benchtop sizes of 15 L, but their high cost ($2500 and up) is prohibitive. This article describes how to construct a bioreactor at virtually no cost, in which one can grow 1-2 L of cells to densities of 4 x 109/mLor more. The design is similar to commercially available reactors but is made out of materials available in most chemistry or biology laboratories. Its basis is the use of a copper heatexchange coil fed from a controlled temperature water bath. The system wmprises a large glass jar, (an institutional size pickle or mayonnaise jar is ideal) with a tightfitting rubber stopper. Through this stopper numerous holes are bored to provide access for:
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the input and output of the heating coil supply a sterile filtered aeration input. a vent tuhe. (prcfernhly fitted with a filter to prevent esrape ufurgonasrns lnto !he mvironment., and optionally: a thermometer to monitor the internal temperature, (a removable adhesive aquarium thermometer attached to the outside is excellent), a system to remove small samples from the reactor to monitor its growth.
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Extra holes can be plugged using short lengths of glass rod. The whole is connected to a circulating water bath, an air supply from an aquarium pump, and placed on a magnetic stir plate. The figure presents a diagram of the complete system. The heat exchanger is a length of 114-in. i.d. copper tubing, (purchased for a couple of dollars from a hardware store.) This tubing is bent around a suitable form, a parallel-sided cup or glass, into a coil of two or three turns, which will fit through the opening into the jar. The ends of the tubing must be bent carefullv unward so thev can be fed throuih the stopper to the oukde. When inseked into the iar the coils should reach close to the bottom but not intekere with the stir bar. The ends of the tubing are connected on the outside to a system that can pump heated water through the coil. The easiest way to do this is with a "Lauda" type circulating water bath, but if this is not available, one can use a regular water bath and pump the water through the coil and 'Fulther details on the use of this system are available from the author.
Comoonentsof Bioreactor back into the bath using an aquarium pump. In either case the idea is to circulate warm water of a reeulated temnerature from a water bath through the hea
