Bacteriophage
Bacteriophage
Phages as valuable molecular tools
Bacteriophage (also known as phages) are viruses that target and infect only bacterial cells. The first observation of what turned out to be bacteriophage was made in 1896. Almost twenty years later, the British bacteriologist Frederick Twort (1877–1950) demonstrated that an unknown microorganism that could pass through a filter that excluded bacteria was capable of destroying bacteria. He did not explore this finding in detail, however. In 1915, the French Canadian micro-biologist Felix d’Herelle observed the same result, and named the microorganism bacteriophage (bacteria eater, from the Greek phago, meaning to eat).
Many types of bacteriophage have been identified since their discovery in 1915, and they are named according to the type of bacteria they infect. For example, staphylophages are specific viruses of the staphylococcal bacteria, and coliphages specifically infect coliform bacteria.
Bacteriophage are the most thoroughly studied and well-understood viruses. They occur frequently in nature, carry out similar biological functions as other viruses, yet do not target human cells for infection. Phages have proven to be a valuable scientific research tool for a variety of applications: as models for the study of viral infectious mechanisms, as tools of biotechnology that introduce new genes into bacterial cells, and as potential treatments for human bacterial infection. For example, the experiments that lead to the
discovery of messenger ribonucleic acid, one of the keys to the manufacture of protein in bacteria, viruses, and even cells found in humans, were accomplished using a bacteriophage. Another example is the bacteriophage designated T4, which specifically infects the bacterium Escherichia coli. T4 has been a cornerstone of molecular biology; studies of the way T4 makes new copies of itself has revealed a great deal of information about bacteriophage genetics and the regulation of the expression the gene viral genetic material. Additionally, another bacteriophage, called lambda, has been fundamentally important to molecular biology as a model system for gene regulation and as a means of moving genetic material from one bacterium to another.
Bacteriophage structure
Bacteriophage have different three-dimensional shapes (or morphologies). Those that are known as T-even phages (i.e., T2, T4, and T6) have a shape similar to the Apollo spacecraft that landed on the Moon in the 1960s. These phages have a head that has a slightly spherical shape called an icosahedron. A tube connects the head to spider-like supporting legs. This overall shape is vital to the way T-even bacteriophage deliver their payload of genetic material into a bacterial cell. Once on the surface on a bacterium, the tube portion of the phage contracts, and the phage acts like microscopic hypodermic needles, literally injecting the genetic material into the bacterium.
Other bacteriophage can be spherical (e.g., PhiX174, S13) or long and threadlike (e.g., M13).
Structurally, bacteriophage, like most viruses, are composed of a protein coat surrounding a core containing DNA (deoxyribonucleic acid) or RNA (ribonucleic acid), though many variations on this basic design exist. The bacteria these viruses infect often measure about one micron in diameter (a micron is one thousandth of a millimeter) and the phages themselves may be as small as twenty-five thousandths of a micron. Bacteriophage infect their hosts by binding to the wall of the bacterial cell. The wall is perforated by enzyme action and phage DNA is injected into the cell. The genetic machinery of the cell is altered to make more bacteriophage DNA. Ultimately, the host cell dies when phage copies accumulate to the point of lysing (bursting) the cell membrane and releasing the phages, which go forth and continue the cycle.
Phages as valuable molecular tools
Much of what has been learned about the mechanisms of viral infection in general has been discerned through the study of bacteriophage. They have proved to be valuable molecular tools for biotechnology, as they can be used as vehicles to move genetic material from one organism into another organism.
It is through this revolutionary use of phages to introduce foreign DNA into new cells that human insulin was first safely and cheaply produced. In a process called lateral gene transfer, genes from one source are transplanted into a different living cell so that they will give the different cell a new characteristic (found in the first cell). For example, specific human genes are implanted in bacterial cells with the aid of phages that allow bacterial cells to produce human insulin and other valuable protein products in great purity and quantity. Lateral gene transfer has given a new, human characteristic to bacterial cells. Bacteriophage act as the deliverers of transferred genes.
Today, bacteriophage used to inject DNA into host cells for research or biotechnology can be “manufactured” in test tubes. Kits containing bacteriophage proteins and structural components are used to create intact phages from pieces that spontaneously self-assemble under the right chemical conditions. In this way, scientists can customize bacteriphage and the DNA they contain for many uses.
Additionally, bacteriophage are only now beginning to fulfill the dream of Felix d’Herelle, in combating infection in humans and animals. The medical potential of many bacteriophage is great as a treatment for blood infection and meningitis for example, along with a host of bacterial infections increasingly resistant to antibiotics.
Bacteriophage therapy is also being explored as a means of curbing bacterial diseases without the use of antibiotics. While antibiotic resistance is possible and,
KEY TERMS
Bacteriophage— A virus that infects bacteria.
Icosahedron— A 20–sided polyhedron.
indeed, is occurring at greater frequency over time, resistance to bacteriophages is remote. Originally explored at the Eliava Institute of Bacteriophage, Microbiology, and Virology in the Russian Republic of Georgia over 70 years ago, bacteriophage therapy fell into disfavor. However, research interest was rekindled in the 1990s. As of 2006, bacteriophage therapy still remains experimental. However, its benefits and potential are promising.
See also Ebola virus; Epstein-Barr virus; Retrovirus.
Resources
BOOKS
Abedon, Stephen T., and Richard L. Calendar. The Bacteriophages. Oxford: Oxford University Press, 2005.
Hausler, Thomas. Viruses vs. Superbugs: A Solution to the Antiiotics Crisis? New York: MacMillan, 2006.
Kutter, Elizabeth, and Alexander Sulakvekidze. Bacteriophages: Biology and Applications. Boca Raton: CRC, 2004.
Brian Hoyle
Bacteriophage
Bacteriophage
Bacteriophage (also known as phages) are viruses that target and infect only bacterial cells. The first observation of what since turned out to be bacteriophage was made in 1896. Almost twenty years later, the British bacteriologist Frederick Twort demonstrated that an unknown microorganism that could pass through a filter that excluded bacteria was capable of destroying bacteria. He did not explore this finding in detail, however. In 1915, the French Canadian microbiologist Felix d'Herelle observed the same result, and named the microorganism bacteriophage (bacteria eater, from the Greek phago, meaning to eat).
Many types of bacteriophage have been identified since their discovery in 1915, and they are named according to the type of bacteria they infect. For example, staphylophages are specific viruses of the staphylococcal bacteria, and coliphages specifically infect coliform bacteria.
Bacteriophage are the most thoroughly studied and well-understood viruses. They occur frequently in nature, carry out similar biological functions as other viruses, yet do not target human cells for infection . Phages have proven to be a valuable scientific research tool for a variety of applications: as models for the study of viral infectious mechanisms, as tools of biotechnology that introduce new genes into bacterial cells, and as potential treatments for human bacterial infection. For example, the experiments that lead to the discovery of messengerribonucleic acid , one of the keys to the manufacture of protein in bacteria, viruses, and even cells found in humans, were accomplished using a bacteriophage. Another example is the bacteriophage designated T4, which specifically infects the bacterium Escherichia coli . T4 has been a cornerstone of molecular biology ; studies of the way T4 makes new copies of itself has revealed a great deal of information about bacteriophage genetics and the regulation of the expression the gene viral genetic material. Additionally, another bacteriophage, called lambda, has been fundamentally important to molecular biology as a model system for gene regulation and as a means of moving genetic material from one bacterium to another.
Bacteriophage structure
Bacteriophage have different three-dimensional shapes (or morphologies). Those that are known as T-even phages (i.e., T2, T4, and T6) have a shape similar to the Apollo spacecraft that landed on the Moon in the 1960s. These phages have a head that has a slightly spherical shape called an icosahedron. A tube connects the head to spider-like supporting legs. This overall shape is vital to the way T-even bacteriophage deliver their payload of genetic material into a bacterial cell . Once on the surface on a bacterium, the tube portion of the phage contracts, and the phage acts like microscopic hypodermic needles, literally injecting the genetic material into the bacterium.
Other bacteriophage can be spherical (e.g. PhiX174, S13) or long and thread-like (e.g., M13).
Structurally, bacteriophage, like most viruses, are composed of a protein coat surrounding a core containing DNA (deoxyribonucleic acid ) or RNA (ribonucleic acid), though many variations on this basic design exist. The bacteria these viruses infect often measure about one micron in diameter (a micron is one thousandth of a millimeter) and the phages themselves may be as small as twenty-five thousandths of a micron. Bacteriophage infect their hosts by binding to the wall of the bacterial cell. The wall is perforated by enzyme action and phage DNA is injected into the cell. The genetic machinery of the cell is altered to make more bacteriophage DNA. Ultimately, the host cell dies when phage copies accumulate to the point of lysing (bursting) the cell membrane and releasing the phages, which go forth and continue the cycle.
Phages as valuable molecular tools
Much of what has been learned about the mechanisms of viral infection in general has been discerned through the study of bacteriophage. They have proved to be valuable molecular tools for biotechnology, as they can be used as vehicles to move genetic material from one organism into another organism.
It is through this revolutionary use of phages to introduce foreign DNA into new cells that human insulin was first safely and cheaply produced. In a process called lateral gene transfer, genes from one source are transplanted into a different living cell so that they will give the different cell a new characteristic (found in the first cell). For example, specific human genes are implanted in bacterial cells with the aid of phages that allow bacterial cells to produce human insulin and other valuable protein products in great purity and quantity. Lateral gene transfer has given a new, human characteristic to bacterial cells. Bacteriophage act as the deliverers of transferred genes.
Today, bacteriophage used to inject DNA into host cells for research or biotechnology can be "manufactured" in test tubes. Kits containing bacteriophage proteins and structural components are used to create intact phages from pieces that spontaneously self-assemble under the right chemical conditions. In this way, scientists can customize bacteriphage and the DNA they contain for many uses.
Additionally, bacteriophage are only now beginning to fulfill the dream of Felix d'Herelle, in combating infection in humans and animals. The medical potential of many bacteriophage is great as a treatment for blood infection and meningitis for example, along with a host of bacterial infections increasingly resistant to antibiotics .
See also Ebola virus; Epstein-Barr virus; Retrovirus.
Resources
books
Flint, S.J., L.W. Enquist, R.M. Krug, et al. Principles of Virology: Molecular Biology, Pathogenesis, and Control. Washington, DC: American Society for Microbiology Press, 1999.
Stahl, F.W. We Can Sleep Later: Alfred D. Hershey and theOrigins of Molecular Biology. Cold Spring Harbor, NY: Cold Spring Harbor Press, 2000.
Summers, W.C. Felix d'Herelle and the Origins of MolecularBiology. New Haven: Yale University Press, 2000.
Brian Hoyle
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Bacteriophage
—A virus that infects bacteria.
- Icosahedron
—A 20–sided polyhedron.
bacteriophage
bacteriophage
bacteriophage
bacteriophage
bacteriophage
bac·te·ri·o·phage / bakˈti(ə)rēəˌfāj/ • n. Biol. a virus that parasitizes a bacterium by infecting it and reproducing inside it.