Beginners Introduction to Bacteriophages

Bacteriophages are viruses which attack bacteria. We do not know of any bacteriophage which attacks fungi, plants, animals, or humans. Since Escherichia coli is a harmless bacterium which grows in the gut of all humans, we often use strains of E. coli as the host and look in sewage for phages which attack the strain of E. coli which we have choosen. Some strains of E. coli can cause diarrhea and thereby cause illness or death. There is no reason for beginners to use pathogenic strains of E. coli. The best known strains of coliphages are grown on non-pathogenic strains of E. coli.

Phage is a common abbreviation of bacteriophage. Coliphages attack E. coli. Bacilliphages attack strains of Bacillus. There are phages which attack fungi, algae, and most species of bacteria. Since a great deal is known about the genetics of certain E. coli strains and the genetics of the coliphages which attack them, the beginning student may learn more if he chooses to work with the well known coliphages and hosts whose genetics is well known. Some of this may be available soon from this website.

Bacteriophages are viruses. Viruses are genetic matter packed inside a protein coat. Some viruses contain a little lipid (fat) or traces of other substances. Viruses are not cells. They are tiny particles that multiply only inside living cells. The experiments on this website will enable you to study the life cycle of typical bacteriophages. There are two main types of phage life cycles: virulent and lysogenic. A virulent phage infects a cell and uses the metabolic pathways of the cell to make a few hundred full-sized offspring and then the cell breaks open releasing the progeny. A lysogenic phage infects a cell and just exists there and multiplies just enough so both daughter cells carry the virus. Under certain conditions a lysogenic virus becomes virulent and the cell opens letting out hundreds of progeny. Other phages have an intermediate life cycle in which progeny are produced constantly and the progeny escape thru the cell wall without causing much damage to the host cell. Animal cells have similar life cycles. Therefore, you can learn a lot about human viruses by sudying bacteriophages.

Lysogenic phages can have important effects without destroying the host cells. Many pathogenic bacteria become harmless then they lose their lysogenic virus. For example, the lockjaw bacterium Clostridium tetani is harmless unless it carries certain viruses. The toxin produced by a pathogenic strain depends upon which virus it carries. The same is true of the Diptheria bacterium. Thus, phages have some medical importance. Phages are also used to type (identify) bacteria strains. Some people still hope that phages can be used to kill pathogenic bacteria but that has never been very useful--see the novel Arrowsmith by Sinclair Lewis.

It is usually possible to isolate a large number of different "species" of phages able to grow inside any given strain of bacteria. A given phage strain may be able to grow inside several strains of bacteria but not inside other strains which to microbiologists seem to have similar traits. Isolating phages from soil, mud puddles, and sewage is usually very easy and makes interesting projects for K-12 students and amateur scientists. Such methods will be given in this web site.

While one must use aseptic methods to maintain his master stocks of bacteria hosts, many phage experiments do not require the use of sterile materials. In fact, experienced phage workers do not use sterile materials for certain experiments. Some phages are inactivated (killed) by drying and you should use those for your projects. Phages which survive drying can be a real problem as they may contaminate everything in your lab and ruin your experiments and all the experiments in the building. When I get such a phage, I autoclave or scrub everything and let everything dry out while I vacation in the library for a couple days. When I returned, everything was always OK. That has happened to me only about once per about 500 to 1000 working days during my career of 15 years working full time with phages. If you spend lots of time isolating new phages from nature, you may have more troubles with "weed" phages than I did.

Phages are very useful in genetics studies because a mating can be completed and the progeny counted in one to a few days. Some very simple methods for crosses and complementation tests have been developed.

The above paragraphs are meant as an introduction and you may not understand much of it because I did not give all the details. The other pages of this website will provide a better understanding by giving more details and experiments which teach the details of bacteriophage life cycles, structure, genetics, and other fascinating aspects of phage biology.

There are many routine bacteriological methods which you will use in your study of phages. Please refer to my bacteria website for methods for isolating bacteria, preparing media, and other details. To work with phages it is a great help to have agar, tryptone, a few mL of chloroform, culture tubes, and petri plates. I will try to help you find substitutes, but it may be better to spent $10 on basic supplies. You may also find it worthwhile to buy a few standard bacterial hosts and a few standard phages and famous mutants if you can't find them free. It is possible to repeat some famous experiments without buying anything. If there is enough interest, I will try to make available some cheap phage kits for beginners for $10 to $25.

You may send private e-messages to Dr. Eddleman and he will reply, usually within 24 hours.

First installed January 1999      Revision #1 1999 Jan 4
Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
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