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The bacteriophages, those viruses that are parasitic on bacteria, are objects of great interest to both the research scientist and to the beginning student of biology. Their extremely minute size, their borderline position between the living and the lifeless, and the tremendous speed with which they reproduce within their bacterial hosts all make them objects to engage the imagination and the intellectual interest of most biology students. In addition, the bacteriophages are not pathogenic to man and are relatively easy to grow in the laboratory with limited and inexpensive equipment. They can be used to demonstrate how scientists can handle and count particles too small to be seen with ordinary microscopes. Further, they and bacteria are praticallv the only organisms that can be used to demonstrate in the laboratory the way in which natural selection works in eliminating the unfit organisms and in selecting those mutant types that are fittest to survive-all within a twentyfour hour period. For these reasons the bacteriophages are a rich source of laboratory material for both the biology teacher and for the ambitious student who wants to do an individual project in the biological laboratory. Both the teacher and the student will be well repaid for learning the few techniques necessary to handle them in the laboratory. The experiments described in this article were suggested and developed by Professor Dean Fraser, Bacteriology Department, Indiana University. They were tried out by the writer and adapted for high school use in the bacteriology laboratory at Indiana University during the summer of 1959. The experiments are designed to require a minimum of equipment and to allow considerable flexibility and margin for errors. The actual materials and equipment needed are the following: six-ounce prescription bottles with screw caps (such as those used by druogists), about twenty-four medicine droppers with bulbs (or home-made pipettes, made from glass tubing, or a few graduated pipettes in sizes 0.1 ml., 1.0 ml., and 5.0 ml.), one transfer needle and one transfer loop each made of either Nichrome or platinum wire set in a metallic handle, sterile petri dishes each containing about twenty mls. of sterilized nutrient agar, sterilized test tubes with either cotton plugs or with metal caps, an autoclave or pressure cooker for sterilizing agar and broth and glassware, a refrigerator in which to store the cultures of virus and of bacteria, or some other means of keeping the cultures refrigerated. An incubator is desirable since it greatly shortens the time required for growing the cultures and gives more consistent results because its temperature is constant. However, if no incubator is available, the cultures, both viral and bacterial, can be grown at room temperatures ranging from 700-800 F. All of these experiments were tried at room temperature and were found to give satisfactory results. A jar or tray of disinfectant into which the used droppers or pipettes can be dropped is also needed. Nutrient agar and nutrient broth can be prepared from formulae and can be sterilized, but this is quite time consuming. Bottles of prepared and sterilized agar and broth can be purchased at very nominal cost (e.g., Difco) and save a great deal of time and labor. If sterile plastic petri dishes are used the time and work of cleaning them for reuse is eliminated, since they are simply flooded with disinfectant and discarded. A glass sDreader made by bending glass rodding (e.g., 3 mm. diameter) is used for spreading plates. Finally, a stock culture of the bacteria, Escherichia coli, Strain B, and also a culture of T1 bacteriophage at a concentration of about 10" particles per ml. are needed.1 When the |
